Texas will have a press conference later in the day to announce the deal.
Hamilton was quite a feel-good story early last season. Acquired by Cincinnati from Tampa Bay via a Rule 5 Draft trade, the 26-year-old -- who had been troubled throughout his career as a professional by drug and legal problems -- got off to an impressive start.
A sprained wrist and a hamstring injury caused him to miss a good chunk of the second half of the season. He finished the season with a .292 batting average and had 19 home runs and 47 RBIs in 90 games.
The hard-throwing, 24-year-old Volquez fanned 166 batters while going 14-6 at three Minor League stops last season.
Herrera, 23, appeared in seven games for Class A Bakersfield and 34 games for Double-A Frisco. All of his appearances for Frisco were in relief, and he allowed 43 hits and struck out 64 in 52 1/3 innings.
T.R. Sullivan is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.