Is Oneness Pentecostalism biblical?

According to the Dictionary of Pentecostal and Charismatic Movements (DPCM), "Oneness Pentecostalism (OP) is a religious movement that emerged in 1914 within the Assemblies of God (AG) of the early American Pentecostal movement, challenging the traditional Trinitarian doctrine, and baptismal practice with a modalistic view of God, a revelational theory of the name of Jesus, and an insistence on rebaptism in the name of the Lord Jesus Christ,"

First, Oneness Pentecostals believe that unless you are baptized using the correct formula you are not truly saved. In their view the formula is, "I baptize you in the name of Jesus" not "I baptize you in the name of the Father, Son, and Holy Spirit." Conversely, when Peter says we are to be baptized "in the name of Jesus" (Acts 2:38) or when Jesus says we are to baptize "in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19), they were not prescribing different formulas. Rather, they were saying that we are baptized by the authority vested in the one true God revealed in Scripture. Thus to be baptized in the name of Jesus is to be baptized on the basis of our belief in his death, burial, and resurrection. By way of analogy, when a police officer commands someone to "stop in the name of the law" the power is not in the phrase, but in the authority it signifies. Likewise, when a physician provides someone who is sick with a prescription, their trust is not in the paper on which it is penned, but rather the potion to which it points. So it is with baptism. The power is not in a prescribed formula but in the heavenly physician to whom the act of baptism points. Baptism is not essential for salvation; it is, however, essential to obedience.

Furthermore, error begets error; thus the belief that one must be baptized only in the name of Jesus has led Oneness Pentecostalism to the further error that Jesus is himself the Father, the Son, and the Holy Spirit. They do not hold to one God revealed in three persons who are eternally distinct but to three manifestations of one God revealed in Jesus. Indeed, according to Oneness, the doctrine of the Trinity is pagan polytheistic philosophy. In truth, the Trinity is neither pagan polytheism nor pagan philosophy. Rather it is biblically based. Scripture plainly reveals personal self–distinctions within the Godhead. As such, the Father says of the Son, "Your throne, O God will last for ever and ever" (Hebrews 1:8 ); and the Son says of the Father, "I am one who testifies for myself; my other witness is the father, who sent me" (John 8:18 ).
Moreover, the very fact that Jesus prays to the Father demonstrates that Jesus cannot be the Father. While I am frequently told by Oneness adherents that this is explained by the notion that Jesus’ human nature prays to his divine nature this is clearly not the case—natures can’t pray, only persons can.

Finally, Oneness Pentecostalism holds to a litany of legalistic proscriptions including the test of rebaptism by their formula with evidence of speaking in tongues. No tongues, no salvation. As one can imagine, this has placed tremendous socio–psychological pressure on adherents to conjure up the gift of tongues. Those who do not speak in tongues are thought to be lacking in faith or even to be entirely unrepentant. In sharp distinction, the Bible relates baptism in the Spirit to empowering for service (Acts 1:5–8 ) rather than evidence for salvation. In the words of Jesus to his disciples, "You will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth" (Acts 1:8 ). The disciples were not still awaiting salvation; rather, they awaited a special anointing of the Holy Spirit that would serve as evidence that their evangelistic message was not of men, but of God (cf. Acts 2:14–21; 1 Corinthians 14:22).

--Hank Hanegraaff | The Complete Bible Answer Book

"Then Jesus came to them and said, ‘All authority in heaven and on earth has been given to me. Therefore, go make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age'(Matthew 28:18–20).