British gas producer BG Group
The discovery made at the Jodari-1 well in block 1 had recoverable mean resource estimated at 3.4 trillion cubic feet (TCF)), above the mean estimate of 2.2 TCF, Africa-focused oil and gas firm Ophir Energy said in a statement.
Ophir, backed by steel magnate Lakshmi Mittal, said the cumulative discovered, recoverable gas resources in blocks 1, 3, 4 were now about 7 TCF.
Ophir holds 40 percent of the three blocks.
3.4 TCF recoverable at Jodari is the strongest possible start to the five-well 2012 Tanzania drilling campaign, Investec's Stuart Joyner said.
This is a very strong start to our five-well 2012 Tanzania drilling campaign and the Metro-1 drillship will now move to drill Mzia-1, which is targeting mean recoverable resources of 4.6 TCF, Ophir said.
BG's shares were up about 1 percent at 1505 pence at 09:30 a.m. British time, on Monday on the London Stock Exchange, while those of Ophir rose 15 percent to 461.7 pence.
(Reporting by Brenton Cordeiro in Bangalore; Editing by Don Sebastian)