Two gallons of oil-based drilling fluid spilled into Cook Inlet during a drilling operation aboard Hilcorp’s Steelhead Platform on Monday after a burst hose on the drill rig released two hundred gallons of the fluid into the platform.

The drilling fluid — also known as drilling mud — was 85 percent diesel and mineral oil, according to Alaska Department of Environmental Conservation public information officer Candice Bressler. Bressler wrote in an email that DEC has requested a safety data sheet about the fluid, and was unable to say whether its other components are hazardous. 180 gallons of the substance were contained on the rig deck, while 18 gallons ended up in the platform’s drill deck and heliport, Bressler wrote.

Hilcorp was required to report the release to DEC because the substance was oil-based, Bressler wrote, which Hilcorp did after the release occurred on Monday. She wrote that DEC officials spoke with a Hilcorp representative by phone and “determined a site visit and additional cleanup efforts were not needed” and did not issue a public notice of the incident because “there was no threat to public safety.”

Hilcorp spokesperson Lori Nelson wrote that technicians from the non-profit oil spill organization Cook Inlet Spill Response and Prevention, Inc (CISPRI) responded to the incident and that “clean up efforts are completed and all necessary repairs and inspections were done before returning to normal operations.”

The Steelhead platform — located in the offshore Trading Bay oil field, north of west Cook Inlet’s Kustaten Peninsula — is among the fifteen Cook Inlet platforms that Hilcorp owns, and one of the newest, having been built in 1986, according to an information sheet from Cook Inlet Regional Citizens Advisory Council.