Pipeline bottlenecks have vexed North American oil producers this year. : HOUSTON/CALGARY, Alberta, May 24 (Reuters) - Pipeline bottlenecks have vexed North American oil producers this year, but for companies making a little-known additive called drag-reducing agent (DRA), they have provided a veritable windfall. DRA is injected into pipelines to reduce the contact between the oil and the wall of the pipe, allowing more crude to flow through.