Mobil Oil New Zealand have pleaded guilty to an oil spill in Tauranga Harbour earlier this year.

The guilty plea was entered during a call-over in Tauranga District Court today.

April's oil spill polluted the upper harbour. Photo: File.

It is the result of a prosecution by the Bay of Plenty Regional Council.

A small hole in a spur line off the main under-wharf bunker line leaked an estimated 1.5 cubic metres of heavy fuel oil into the water on April 27.

Carried by wind and the tide, the slick polluted the Tauranga Bridge Marina, as well as the upper harbour at Maungatapu.

Clean up costs are said to be $1.79 million, and Mobil's next appearance is on March 14, 2016.

Mobil may be sentenced on that date, but that will depend on other matters such as whether a restorative justice meeting has occurred with affected parties and whether Mobil agrees with the Regional Council's summary of facts for the prosecution.

Both parties are expected to meet at sentencing but that is dependent on whether a restorative justice meeting with iwi has taken place by then.