Charles Ellicott Commentary Numbers 23:2

"And Balak did as Balaam had spoken; and Balak and Balaam offered on every altar a bullock and a ram." — Numbers 23:2 (ASV)

And Balak and Balaam offered.— It is more probable that Balak, as a king, performed priestly functions than that Balaam performed them alone. (See Note on Numbers 22:40.)