This research investigated and evaluated the concept and manifestations of Spirit baptism in selected Pentecostal denominations in Oyo State. Both theological and empirical evaluations were made on the four denominations which were randomly selected for the study. The instruments used were questionnaire, observation and interview. In all, 416 copies of questionnaire were sent out and 402 copies were returned. Of these, only 393 were found usable for the research. Two Pentecostal churches that belong to two of the four denominations studied in Oyo state were personally observed by the researcher. Then, three Oyo State heads of the four denominations studied were interviewed. The Oyo state head of the fourth Pentecostal denomination that could not be interviewed had been transferred and had not been replaced when this research was carried out. For the analysis of data, frequency, percentage, Ttest and ANOVA were used as appropriate. The findings of the research are that: 1. The Pentecostal define Spirit baptism as the initial infilling of the Spirit subsequent to salvation. 2. The Pentecostal view the signs of Spirit baptism to be: speaking in tongues, ecstaticism, feeling of joy, the reception of physical healing and the ability to perform miracle. Of these however, speaking in tongues is the most important. 3. To the Pentecostal, the techniques of invoking Spirit baptism are: abstaining from sin, hearing of soul inspiring messages on Spirit baptism, and series of intense praying. The Pentecostals are convinced that the experience they term "Spirit baptism" brings about changes in a person's life-style. Statistical tests reveal that there is no significant difference between the church members and the church ministers in their opinions on the signs of Spirit baptism, and that there is also no significant difference among the selected denominations in their opinions on the relationship of Spirit baptism to changed life-style. The differences in the responses of men to women, church ministers to church members, denomination to denomination on the concept of Spirit baptism are however significant. Significant differences were also discovered between the male and the female respondents, and among the selected denominations on the manifestations of Spirit baptism. Through evaluation, the bases for first two findings that: Spirit baptism is initial infilling of the Spirit subsequent to Salvation; and that the sign of Spirit baptism are speaking in tongues, ecstaticism, feeling of joy, reception of physical healing and the ability to perform miracles, were found to be theologically questionable, while the last two findings that: the techniques of invoking Spirit baptism are abstaining from sin, hearing of soul inspiring me�sages on Spirit baptism, and series of intense praying; and that the Pentecostals opine -that the experience of Spirit baptism brings about changes in a person's lifestyle could be justified theologically if only the Pentecostals would accept to change their use of the term "Spirit baptism" to Spirit infilling in the two contexts