By Iain Packham

LONDON--Gulf Keystone Petroleum Ltd. (GKP.LN) said Thursday its consultants have significantly increased the estimated gross oil-in-place volumes for the Shaikan field in the Kurdistan region of Iraq, completing the appraisal program.

The consultant, Dynamic Global Advisors, estimates the field holds between 12.4 billion barrels and 15 billion barrels, up from the previous estimate of 8.0 billion to 13.4 billion barrels of oil.

The upgrade is based on the data acquired since the last resource evaluation of the Shaikan discovery by DGA in November 2011 and is the fourth successive upward revision since the Shaikan discovery was announced in August 2009.

Gulf Keystone will now submit a Declaration of Commerciality to the Ministry of Natural Resources of the Kurdistan Regional Government, under the terms of the Production Sharing Contract regarding the Shaikan block. This Declaration of Commerciality will be followed by the submission of an Appraisal Report within two months.

Gulf Keystone is the operator of the Shaikan block with a 75% working interest and is partnered with MOL Nyrt. (MOL.BU) and Texas Keystone Inc., which have a 20% working interest and a 5% working interest, respectively. Texas Keystone Inc. holds its interest in trust for Gulf Keystone, pending transfer of its interest to the company.

Shares closed Wednesday at 212.25 pence.

Write to Iain Packham at iain.packham@dowjones.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires