Property and liability premiums for drilling platforms have risen sharply in the wake of the Deepwater Horizon oil spill, according to Moody’s Investors Service.

The ratings agency says property lines have responded to the disaster with rises of between 15-25% for rigs operating in shallow waters and up to 50% higher for deepwater rigs.

The April 20 oil well blowout in the Gulf of Mexico killed 11 platform workers and created a massive slick that some analysts suggest could cost more than $US10 billion ($12.2 billion) in cleanup costs.

Claims are likely to follow from marine hull, marine liability, general liability, environmental/pollution liability, control of well, directors’ and officers’, business interruption (BI) and workers’ compensation lines.

Moody’s Vice President James Eck says the spill will have a substantial impact on the market for offshore energy-related insurance coverage.

“Pricing for offshore energy liability insurance will likely also trend higher as insurers and reinsurers take stock of their losses and re-evaluate the complex risks associated with drilling in deep waters,” he said.

Mr Eck says potential BI claims “represent the largest unknown for insurers”.