Virtually every commentator on Romans 8:26 agrees that the Spirit's intercession is a direct inaudible communication between the Spirit and the Father, transforming the frustrated prayers of believers. Quite a few have specifically commented on the idea that it is tongues:
Romans - Thomas R. Schreiner (Professor of New Testament Interpretation, Southern Baptist Theological Seminary.)
Despite the appeal of seeing a reference to glossolalia, there are decisive reasons for rejecting this interpretation. The term ἀλαλήτοις could mean that which cannot be uttered in words, but it much more likely means "without speech," the absence of any vocalization at all. This seems to be the most natural way of translating a word that negates a word for speech. (2) The word στεναγμοῖς is not necessarily meant literally; that is, the groaning may not be audible. That groaning may be metaphorical is evident from the reference to the groaning of creation in verse 22. Indeed, the groaning in verse 26 must be metaphorical in some sense because the text says that it is the "Spirit" who groans. Nowhere else in the Bible does the Holy Spirit audibly groan, and thus a literal meaning here is not likely, One might reply that the Holy Spirit's groaning is expressed through the groaning of believers (cf. Rom. 8:15-16; 1 Cor. 14:14-15). This is probably the case, but even in that case the groaning is not necessarily audible. The point could be that believers have longings that are so deep that they are inexpressible. (3) The most serious objection to a reference to tongues speaking is that Rom. 8:26-27 refers to all Christians, while tongues speaking is reserved to only a few." There is no evidence in verses 26–27 that any believers are excluded from the assistance of the Spirit described here. Indeed, it would destroy the entire argument of chapter 8 if any believers were outside the pale of what Paul says. Fee thinks this argument is a weak one and says that texts in 1 Cor. 12-14 resolve the difficulty. He apparently refers to the texts that say believers should earnestly desire spiritual gifts (1 Cor. 12:31; 14:1) and all should desire to speak in tongues (14:5). It is mystifying to me how he thinks that this solves the problem. Let us take Paul's words in 1 Cor. 14:5 at face value and assume that Paul desires all Christians to speak in tongues. Even so, Fee's argument can prevail only if all believers did in fact speak in tongues. First Corinthians 12:30 testifies that not all did so. Alternatively, Fee would have to argue that the Spirit's assistance described in Rom. 8:26-27 is available only to those with the gift of glossolalia. But we have already seen that Paul did not exclude any believers in this section, which is designed to buttress their hope.
Epistle to the Romans - Douglas J. Moo (Professor of New Testament, Wheaton College)
However, others who ascribe the groans to believers think that Paul is referring to glossolalia—the “speaking in tongues” of 1 Cor. 12–14. Like tongues, these “groans” are a “prayer language,” inspired by the Spirit, and taking the form of utterances that cannot be put in the language of earth. But this identification is unlikely. The gift of tongues is clearly restricted by Paul to some believers only (cf. 1 Cor. 12:30), but the “groans” here are means of intercession that come to the aid of all believers.
Furthermore, and to return to our original point, the word alaletois probably means "unspoken" rather than "ineffable"; and this makes it almost impossible to identify the "groans" with glossolalia; for tongues, of course, are verbalized if not understandable.
Paul's Letter to the Roman - Colin G. Kruse (Professor of New Testament, Melbourne School of Theology)
Some have suggested that Paul is referring to believers' prayers in tongues inspired by the Spirit, but this seems unlikely because: (i) the apostle is speaking of the Spirit's intercession for us, not his inspiration of prayer in tongues by us; (ii) Paul says that the Spirit's intercession is through wordless groans' (lit. 'unspoken groans'), which suggests that the intercession is silent and not oral as is speaking in tongues.
While there is clearly a verbal connection between the groaning of creation, the groaning of believers, and the groaning of the Spirit, the Spirit's groaning is clearly of a different order. In the former cases groaning emanates from frustration or suffering, whereas in the case of the Spirit this is certainly not so — his groaning is associated with intercession for believers.
Romans - C. E. B. Cranfield (Professor of Theology, University of Durham)
On the other side there seems to be force in the contention that the στεναγμοῖ mentioned here are not likely to be the utterances of glossolaly, since they clearly have to do with bringing the needs and longings of Christians before God, whereas glossolaly was pre-eminently praise.' But more decisive is the argument that, coming after the words τὸ γὰρ τί προσευξώμεθα καθὸ δεῖ οὐκ οἴδαμεν (cf. ἐντυγχάνει ὑπὲρ ἁγίων in v. 27), στεναγμοῖς ἀλαλήτοις must refer to the Spirit's own στεναγμοῖ, and it is highly unlikely that Paul would think of the ecstatic utterances of certain Christians, inspired by the Spirit though these utterances might be, as being the Spirit's own στεναγμοῖ.
Romans - James Dunn (Professor of Divinity, University of Durham)
… The thought is therefore of groans not formulated in words. This means that a specific allusion to glossolalia is unlikely, since Paul evidently thought of glossolalia as spoken language, the language(s) indeed of heaven (1 Cor 12:28, 30; 13:1; 14:2, 10–11; cf. particularly T. Job 48.3, 49.2, and 50.1–2; see further Dunn, Jesus, 243-44). It is true that there is an overlap in thought of angel and spirit in Jewish thought (see above); so too sharp a line between heavenly intercession to which Paul will allude shortly in v 34) and the Spirit's intercession on earth should not be drawn. Consequently some have compared the "inarticulate groans" with the "unutterable words" (äppnta pnuata) of 2 Cor 12:4 (e.g., Wilckens). The inappropriateness of the suggested parallel lies not in the words themselves but rather in the sense they express: on the one hand, visions of heaven which leave the mind speechless and, on the other, the wordlessness of complete inability in the entanglements and frustration of all too earthly existence; the one focusing on the indescribable character of what has been seen, the other on the inability of believers in this age to put into words the reality of their own condition and relation to God…. had Paul wished his readers to think of glossolalia he would probably have written with greater care (cf., e.g., Schniewind, “Seufzen,” 82–84
Paul's Letter to the Romans - Ben Witherington (Professor of New Testament Interpretation, Asbury Theological Seminary)
Does stemagmois alaletois refer to sighs that are wordless, or beyond words, or to the inarticulate groans of the ecstatic prompted by the Spirit, or possibly even to glossolalia uttered in worship (1 Cor. 14.14)?' … Cranfield denies that glossolalia is in view here since it is private prayer and praise language while the problem here seems to be bringing the known needs of believers before God in an adequate manner. One might have expected a little more explicitness if glossolalia were in view here. And, most decisively, Paul is talking about the Spirit uttering inarticulate groans, not the believer. Thus Cranfield is probably right that what is meant are utterances or groanings that are imperceptible to the believer. The Spirit groans along with the believer, just as the believer groans as part of fallen creation.
Systematic Theology - Wayne Grudem (Professor of Theology and Biblical Studies, Phoenix Seminary)
i. Is Romans 8:26 - 27 Related to Speaking in Tongues?
Paul does not mention speaking in tongues explicitly here, and the statement is a general one concerning the life of all Christians, so it does not seem correct to say that Paul here is referring to speaking in tongues. He is referring to a more general experience that occurs in the prayer life of every Christian. … There is no explicit mention of our spirit praying (though that may indeed be true as well), nor is there mention of our mind being unfruitful or lacking understanding (though that may at times be at least partially true). Nor do these sighs or groans come forth in anything that could be called “other tongues” or “other languages.” So there are several differences, even though Romans 8:26–27 talks about intercession that we make in sounds that are not fully understood by us, and therefore it is a phenomenon that has some similarities to speaking in tongues.
Romans - Robert Mounce (president emeritus of Whitworth University)
Some who hold that στεναγμοῖς ἀλαλήτοις (“groans that words cannot express”) refers to the groaning of the believer also hold that Paul was referring to glossolalia, speaking in tongues (e.g., E. Käsemann, “The Cry for Liberty in the Worship of the Church,” in Perspectives on Paul [Philadelphia: Fortress, 1971]: 122–37), but that is highly unlikely. ἀλάλητος means “unspoken.”
Romans - Leander E. Keck (Professor of Biblical Theology Emeritus at Yale Divinity School)
Are the groans unspoken because they are unspeakable (NRSV: “too deep for words"), or because they are a form of "tongue-speaking" - uttered sounds that are not spoken words (Fee (1994, 579-85) discusses various possibilities)? Given the recent increase in "Pentecostalism,” it is understandable that much attention has been focused on these "unspoken groans"; the focus of the passage itself, however, is in verse 27, which explains why the Spirit's interceding is the effective help for believers who do not know what they ought to pray.
The explanation assumes that the Spirit resides in the self (v. 9). So God "who searches the heart knows the mindset (phronema, as in v. 6) of the Spirit” (AT), because, presumably, the Spirit resides in the heart. Moreover, the Spirit "intercedes," speaks to God on behalf of those who do not know what to pray, and does so in accord with God (kata theon), that is, in keeping with God's will. The Spirit does not need to persuade God on our behalf (as if it were a lobbyist) because the Spirit speaks in accord with God. In other words, Paul apparently says that the Spirit's intercession transforms our ignorant praying into what is in keeping with God's will. When one compares what is said here about the Spirit with 1 Cor 2:9-16, a significant difference becomes evident: Whereas in the present passage the Spirit communicates to God on our behalf, there the Spirit communicates to us, since the Spirit is the only one that knows "the things of God.” In both passages, the Spirit's role in communication overcomes human limitations, whether by revealing the otherwise unknowable things of God to us or by speaking to God on our behalf.
The Moody Bible Commentary
Groanings too deep for words is an oxymoron, but describes the Spirit's “wordless prayer groaning" on behalf of God's children. Too deep for words means "unspoken," "unspeakable," "unuttered," "unutterable," but in any case these groans are inaudible and therefore do not refer to speaking in tongues. In addition, the Spirit Himself performs this intercessory ministry, but speaking in tongues involves the participation of the believer (cf. 1 Co 14:14), and while not every believer speaks in tongues (1Co 12:30), every believer can be confident of this prayer ministry of the Spirit. If God knows every thought of every person, then He is quite capable of understanding the Spirit's prayers for His children (v. 27).