Pollution represents a massive threat to our oceans. Unfortunately, sea-going vessels contribute to this threat by spilling different kinds of pollutants, in particular oil. A key factor in the efforts to prevent vessel-source pollution is the distribution of powers to legislate and to enforce in the event legislation is breached. Traditionally, these powers have - at least on the high sea - been held by the flag States. But after World War II, the coastal States have been given increasingly more of these powers, a process often referred to as 'creeping jurisdiction'. However, neither prescriptive nor enforcement jurisdiction is sufficient remedy as vessels may be the source of pollution even when complying with comprehensive legislation. Vessel casualties in particular may occur, regardless of such compliance. In principle, only flag States will then have powers over the vessel. However, an affected coastal State may wish to implement measures on a vessel in order to prevent or mitigate pollution. The topic of this study is basically when and by what means coastal States can intervene when maritime casualties pose a threat of pollution. The author was born in 1965, and received his law degree from the University of Oslo in 1990. In 1999 he became dr. juris. He has later held positions as a judge in the Hålogaland court of appeal and as a professor at the University of Tromsø. In February 2010 he was appointed a judge of the Supreme Court of Norway.