R.M. Seeley, director of the federal Pipeline and Hazardous Materials Safety Administration's southwest region in Houston, sent a letter to Exxon Mobil Pipeline Co. President Gary Pruessing stating the regulator agreed to a request for the extension.
"PHMSA has reviewed this request and has no objection to the request for additional time to complete the plan," Seeley's letter read.
The PHMSA letter was dated Oct. 8 and published Tuesday on its website.
Seeley said Exxon has until Jan. 6 to submit its plans to the PHMSA for repairs needed to restart the pipeline.
About 5,000 barrels of a diluted form of heavy Canadian crude oil spilled from a 22-foot rupture in the pipeline in Mayflower, Ark., in March.
Last week, the PHMSA listed nine likely violations of federal safety rules associated with the pipeline, which has the capacity to carry 90,000 barrels of oil per day.
The PHMSA said Exxon may face a civil penalty of $2.65 million for violations associated with the oil spill.