Contracts used by marine contractors in the offshore installation business are normally detailed and large in size. The contracts deals with complex projects and regulates obligations and economic risk between the parties.This thesis is a presentation of the frequently used contracts, SUPPLYTIME 05 and NSC 05, and an identification of contractual economic risks exposed to marine contractors through these two contracts. I am doing a practical contractual economic risk analysis of central clauses in the contracts from the marine contractors’ point of view. The analysis is an identification of differences and a comparison of chosen clauses in these two contracts. Problems of particular interest is late delivery of vessels, off-hire, and pollution. SUPPLYTIME 05 and NSC 05 treat these particular problems differently. Therefore, these problems can be of great interest for marine contractors. Other problems of interest are damage, and variations to the Work. Both contracts have similar, so called knock-for-knock clauses regarding damage. Rules regarding variations to the Work are only covered in NSC 05.This thesis proves that NSC 05 and SUPPLYTIME 05 do not correspond on vital parts and that SUPPLYTIME 05 may not be a preferable contract for marine contractors. Therefore, this thesis also presents alternative contractual advices to marine contractors to avoid risk.