| Year | Month | Event |
|---|---|---|
| 2013 | Jan | Acquired interests in Block 36/4 in the Norwegian North Sea. |
| 2012 | Oct | Acquired interests in Blocks P1939 in the North Sea, UK and Block P2016 and P2024 off the west coast of the Shetland Islands, UK. |
| Jan | Acquired interests in Blocks 31/1, 35/10, 36/7, 34/2, 3, 6, 35/1, 4 in the Norwegian North Sea, Blocks 7120/1, 2 in the Barents Sea, Norway. | |
| 2011 | Feb | Acquired interests in Blocks 35/6,35/7,6202/8,9,6203/7 in the North Sea, Norway. |
| May | Acquired interests in Blocks6601/6,9,6602/4,7,6605/2,3,6,6606/1,6706/10 in the Norwegian Sea, Blocks 7220/6,9,11,12,7221/4,7324/9,7325/7 in the Barents Sea. | |
| 2010 | Jan | Acquired interests in Block 31/2 and Block 34/7 in the North Sea, Norway |
| Feb | Began production at the Nam Rong - Doi Moi field (Block 09-3) offshore Vietnam | |
| Oct | Began production at the Burghley field(BlockP240) the North Sea, UK. | |
| Acquired interests in Blocks P1791、P1800 in the North Sea, UK and Block P1850、P1853 off the west coast of the Shetland Islands, UK. | ||
| Dec | Acquired interests in Blocks P079 in the North Sea, UK. | |
| 2009 | Apr | Acquired interests in Blocks 7324/7, 8 in the Barents Sea, Blocks 6604/2, 3, 4, 5, 6 in the Norwegian Sea and Block 6203/10 in the North Sea, Norway |
| Nov | Acquired interests in 17 licenses (P069, P073, P077, P087, P185, P205, P240, P297, P307, P324, P344, P729, P810, P973, P983, P1047 and P1083) in the North Sea, UK |
|
| 2008 | Jul | Acquired an interest in Block 2/9 in the central area of the Norwegian North Sea, Norway |
| 2007 | Feb | Acquired interests in Block 35/4, 35/5 and Block 35/9 in the North Sea, Norway |
| May | Acquired interests in 4 exploration Blocks (P1165, P1190, P1192 and P1196) off the west coast of the Shetland Islands, UK | |
| Jun | Acquired interests in Blocks 35/7, 10, 34/12 in the North Sea, Norway | |
| 2006 | Jan | Acquired interests in Block 34/2,3,5,6, Block 35/7, and Block 35/12 in the North Sea, Norway |
| Apr | Acquired interests in Block 6505/6, 9, 6506/4 and Block 6506/1 in the Norwegian Sea, Norway | |
| Oct | Began production at the Fram East field (Block35/11) in the North Sea, Norway | |
| 2004 | Jun | Acquired an interest in Block 35/2 in the North Sea, Norway |
| Oct | Acquired exploration rights for Blocks 05-1b and 05-1c offshore Vietnam | |
| 2003 | Oct | Began production at the Fram fields (Block 35/11) in the North Sea, Norway |
| Oct | Began production at the Vigdis East and the Borg Northwest fields (Block 34/7) in the North Sea, Norway | |
| 2002 | Mar | Dissolved Idemitsu Oil Development Co., Ltd. |
| Apr | Acquired an interest in Block 09-3 offshore Vietnam | |
| May | Acquired an interest in the Fram fields (Block 35/11, 35/12, 31/2) in the North Sea, Norway | |
| 2001 | Mar | Idemitsu Oil Development Co., Ltd. transferred all of its interests in the Sea of Japan to Idemitsu Oil & Gas Co., Ltd. |
| Apr | Transferred the interest in the Iwafune-oki oil field offshore Niigata | |
| Jun | Began production at the northern Snorre field (Block 34/4 and 34/7) in the North Sea, Norway | |
| 2000 | Aug | Began production at the Sygna field (Block 34/7) in the North Sea, Norway |
| 1999 | Jul | Began production at the Borg field (Block 34/7) in the North Sea, Norway |
| 1998 | Dec | Began production at the Tordis East field (Block 34/7) in the North Sea, Norway |
| Closed the Aga-oki oil and gas field offshore Niigata | ||
| 1997 | Jan | Began production at the Vigdis field (Block 34/7) in the North Sea, Norway |
| Oct | Acquired an interest in Offshore Cambodia Areas I&Ⅱ | |
| 1996 | Nov | Sold the interest in the Kandawari gas field in Pakistan |
| 1995 | May | Began production at the Kadanwari gas field in Pakistan |
| 1994 | Jun | Began production at the Tordis field (Block 34/7) in the North Sea, Norway |
| Sep | Began production at the Statfjord East field (Block 34/7) in the North Sea, Norway | |
| 1993 | Mar | Closed the Aga-oki-kita oil field offshore Niigata |
| 1992 | Aug | Began production at the southern Snorre field in the North Sea, Norway (Block 34/4 and 34/7) |
| 1990 | Dec | Began production at the Iwafune-oki oil field offshore Niigata |
| 1989 | Aug | Idemitsu Oil & Gas Co., Ltd. established |
| Oct | Acquired interests in the Snorre field in the North Sea, Norway (Block 34/4 and 34/7) | |
| 1984 | Oct | Began production at the Aga-oki-kita oil field offshore Niigata |
| 1976 | Jul | Idemitsu Oil Development Co., Ltd. established (Trade name changed from Idemitsu Japan Sea Oil Development Co., Ltd.) |
| Sep | Began production at the Aga-oki oil and gas field offshore Niigata | |
| 1972 | Feb | Discovered the Aga-oki oil and gas field offshore Niigata |
| 1971 | Jan | Idemitsu Japan Sea Oil Development Co., Ltd. established |