The business units containing the semi submersibles (Offshore Rig Services AS) was registered in May 2005. The vision was to build and operate fit for purpose semi submersible drilling units for drilling in mid water down to 750 meter. In September 2005 Offshore Rig Services awarded the contract for drilling equipment and systems/drilling package to National Oilwell Varco. In November 2005 Offshore Rig Services awarded the construction contract to Yantai Raffles Shipyard, China. Major subcontractors were Siemens, Wärtsilä, Kongsberg Maritime, Global Maritime and DNV.
The first steel cut for the first drilling unit COSLPioneer was celebrated with a ceremony at the yard in June 2006. In August 2006 Offshore Rig Services changed company name to OffRig Drilling ASA.
In February 2007 Awilco Offshore ASA acquired 100% of the shares in OffRig Drilling ASA and the company changed name to Awilco Offshore Semi AS. In April 2007 Awilco Offshore Semi AS was awarded two long term drilling contracts for two semi submersible drilling units by Norsk Hydro Produksjon AS on behalf of the license partners of the Troll Production License for 8 years each plus 8 x 1 year options. In June 2007 Awilco Offshore signed contract for the fourth drilling package with National Oilwell Norway AS.
In July 2008 China Oilfield Services Limited offered to purchase all shares in Awilco Offshore ASA. The purchase was effective from close of trading on Oslo Stock Exchange on 15 October 2008 and then Awilco Offshore ASA was de-listed from the Oslo Stock Exchange. The company changed name to COSL Drilling Europe AS.
After the take-over, COSL Drilling Europe has taken delivery of the three semi-submersible drilling units which were constructed in China and the two accommodation units - COSLRival and COSLRigmar has been operated by COSL from respectively 2010 and 2011.
The three semi submersible drilling rigs were delivered from the yard respectively November 2010 (COSLPioneer), November 2011 (COSLInnovator) and May 2012 (COSLPromoter).
In December 2011 COSL signed the construction contract with CIMC Raffles Offshore to construct our semi-submersible drilling unit no. 4, named COSLProspector. Delivery of this unit from the yard will be in Q3 2014. This yard is the same that has constructed drilling unit no. 1-3.