(Reuters) — U.S. energy companies added oil rigs for a fifth straight week, extending a nine-month recovery as drillers take advantage of crude prices that have held mostly over $50 a bbl since OPEC agreed to cut supplies in late November.

Drillers added six oil rigs in the week to Feb. 17, bringing the total count up to 597, the most rigs since October 2015, energy services firm Baker Hughes Inc. said on Friday.

During the same week a year ago, there were 413 active oil rigs.