Natural marine oil seepage.

The probable range of seepage into the marine environment is 0.2 x 10(6) to 6.0 x 10(6) metric tons per year. Within this range the best estimate for the present marine seepage worldwide is on the order of 0.6 x 10(6) metric tons per year. This estimate is based on the presumption that only a few other areas around the world are as seepage-prone as southern California. Measurements of seeps and seepage rates are too few to allow an accurate estimation by observation and measurement techniques alone. Seepage potential can, however, be related to geologic criteria, and these provide sound bases for marine seepage assessment. On the basis of this estimate, areas of high seepage potential contribute about 45 percent of the worldwide seepage, areas of moderate seepage about 55 percent, and areas of low seepage less than 1 percent. The situation varies somewhat from ocean to ocean. In the Pacific Ocean, areas of high seep potential are by far the major contributors. In the Atlantic, Indian, Arctic, and Southern oceans, areas of moderate seep potential are most significant because areas of high seep potential are relatively rare in these realnis. The circum-Pacific area is the area of greatest seepage; it contributes about 40 percent of the world's total.