U.S. energy firms cut oil rigs for a fourth week in a row this week, data showed on Friday, a sign the continued weak prices were causing energy firms to reduce drilling plans. Drillers removed four oil rigs in the week ended Sept. 25, bringing the total rig count down to 640, the lowest since July, after cutting a total of 31 rigs over the three prior weeks, oil services company Baker Hughes Inc said in its closely followed report. That compared with 1,592 oil rigs in the same week a year ago and an all-time high of 1,609 in October 2014. Combined with the reduction in natural gas rigs, total U.S. rigs were at a 12-year low. Natural gas rigs were down one this week to 197, up just one from its lowest level since at least 1987, according to the Baker Hughes data. […]