Tanzania has been intermittently explored over the last 50 years. Most of the multinational petroleum companies were represented in the area, at one time or another. Significant gas discoveries were made at Songo Songo and Mnazi Bay. So far a total of 35 exploration and development wells have been drilled. The cumulative seismic coverage in public domain is approximately 52,000 km of which 28,000 km were acquired offshore and 24,000 km onshore. The onshore seismic coverage includes coastal as well as interior rift basins. An additional 11,000 km of Deep-sea modern non-exclusive geophysical data were acquired in the year 1999/2000. Although no oil has been produced until now, available data and geological information reveal the existence of an active petroleum system.