Abstract: A towable vertical stacking bale accumulator features angle-adjustable roller beds on an obliquely oriented trailer frame whereby a rearwardly declining slope of the rollers gravitationally conveys individual bales from the baler to a stacking station at the rear of the trailer frame, where an automatically controlled gate provides a stop for retaining the bales until either a full stack is compiled or an error is detected. Spring loaded bale lifters feature concave undersides to encourage retraction of same as they are lowered down the sides of a newly arrived bale, and carry hanging bale guides that prevent the incoming bales from overshooting sides of the roller bed. Lift frames on which the bale lifters are carried are raised and lowered by hydraulically driven lift arms, and are further stabilized by engagement of lift frame followers with guide members of upright support structures provided on opposing sides of the roller bed.