License blocks were first designated by the Spanish administration and offered for international tender in 1965 with awards going to groups operated by Mobil and Spanish Gulf Oil (Spangoc) but the exploration effort led to no commercial success. After independence in 1968, petroleum activity was much reduced and further significant exploration did not occur until after the 1979 change of Government. Hispanoil and the new Government formed a joint venture company, GEPSA, which discovered the Alba gas condensate accumulation in 1983. GEPSA deemed Alba to be non-commercial and their licenses lapsed. During the 1980's, Total and Elf operated groups that explored onshore and offshore Rio Muni where extensive seismic surveys were undertaken and four wells drilled without success.
The Alba acreage was relicensed in 1990 to US independent Walter International who commenced production in 1991 from two new wells. In 1995 Nomeco (subsequently CMS Oil and Gas) acquired Walter and progressively expanded onshore processing capacity to cope with increased production from additional Alba wells. The success of the Estrella-1 well (CMS, 2001), a gas condensate discovery 6 km north of the Alba Field, emphasised the large potential of the Alba Block. All CMS assets were acquired by Marathon Oil in January 2002 and Marathon has continued with investment and expansion of the Alba Field.
In 1992, United Meridian Corporation (UMC, subsequently Ocean Energy / Devon Energy) licensed Blocks A and B and in 1995 licensed Blocks C and D. UMC drilled the unsuccessful Dorado-1 well in Block A and the Delta-1 well in Block B in 1994. In 1995 Mobil farmed-in to Block B and drilled the Zafiro-1 discovery well of the 1.1 billion barrel Zafiro Field. Mobil drilled nine exploration wells in Block B outside of the Zafiro area, with discoveries at Azurita-1 (1997), Berilo-1 (1998), Turmelina-1 (1998) and Esmerelda (2005). Mobil aso farmed-in to Block C in 1999 and drilled the Ostra-1 exploration well, followed by the Oreja Marina-1 exploration well in 2001 and Estrella del Mar-1 in 2002.
During 2000, Ocean Energy relinquished Block A and operatorship of Block D was taken over by CMS (now Marathon). In 2004, Marathon drilled the Corona-1 discovery well in Block D which extended the Alba Field into Block D.
Triton Energy was awarded Rio Muni Blocks F & G in 1997, covering areas previously licensed to Elf and acquired seismic through 1997 and 1998. In late 1999 Triton made a significant discovery with the first well on its licences, Ceiba-1, which tested oil at 12,400 bopd and led to the first production in the Rio Muni basin in November 2000. As a result of the Ceiba discovery, an aggressive exploration programme was undertaken by Triton during 2000 - 2001 that continued after the acquisition of Triton by Amerada Hess in 2001. This exploration campaign resulted in 18 successful wells which proved up several hundred million barrels of oil in northern Block G which were developed as the 'Okume Complex'. The Okume Plan of Development was approved by the MMIE in 2003 and the field came onstream in 2006. Additionally the G-13 discovery was made in southern Block G in late 2002 which was appraised in 2003 but remains undeveloped.
Following a Deep Water Licensing Round in 1998-99, five exploration licenses were signed during 2000 with Atlas Petroleum (Blocks H, I and J), Vanco (Block K) and Chevron (Block L) as operators. Extensive 3D surveys were acquired in these licenses in 2001 and exploratory drilling commenced in early 2003 with the drilling of the unsuccessful L-1 well by Chevron. In 2000 RocOil farmed-in to the Atlas Block H and became Technical Operator. This was followed in 2004 by the farm-in of Pioneer and the drilling of the unsuccessful H-1 well. In 2011 White Rose farmed-in to Block H and took over as Technical operator from Roc Oil. The H-2 exploration well is planned for Q4 2012.
In 2004, Nexen farmed-in to Block K, assumed operatorship and drilled the K-1 well in late 2004 followed by the K-2 well in 2005. In 2005 Petrobras farmed in to Block L and drilled the unsuccessful L-2 exploration well and in 2006 both Chevron and Petrobras withdrew from Equatorial Guinea and Block L was relinquished.
During 2002 new exploration licenses were awarded to the Fruitex Group covering Block M in the western offshore Rio Muni and to a Petronas operated group for Block N covering Corisco Bay. Fruitex acquired 2D and 3D in Block M and in late 2003 Petronas drilled the N-1 well (with non-commercial oil) and the N-2 well in 2005.
In 2003, Devon Energy were awarded Block P in the Rio Muni Basin and in 2004 Noble Energy were awarded Block O and PetroSA Block Q, both in the Douala Basin, offshore Bioko Island. In 2004 Devon Energy drilled the unsuccessful P-1 well but in October 2005 the P-2 well was announced as an oil discovery and was subsequently successfully appraised. In 2008 GEPetrol became operator of Block P when they purchased the Devon Equatorial Guinea assets.
In October 2005 Noble Energy announced that the O-1 well in Block O was a gas condensate discovery, the first discovery in the Equatorial Guinea part of the Douala Basin. The O-1 discovery was appraised by the O-3 and I-4 wells in 2007 and declared a commercial discovery, the Alen Field. The Alen Field Plan of Development was approved in January 2011 and production is anticipated to commence in 2013. In February 2009 Noble Energy announced that the O-5 (Carmen) exploration well was an oil discovery, the first oil discovery in Block O. It is anticipated that this will be developed as a tie-in to the Alen facilities.
In 2004 Noble Energy farmed-in to Block I and took over as Technical Operator and in June 2007 announced that the I-1 exploration well was a gas condensate discovery. In October 2007 Noble announced that the I-2 appraisal well to the I-1 discovery, had encountered oil below the gas condensate found in the I-1 well and in June 2008 announced that the I-5 well had confirmed the downdip extent of the oil leg. In July 2009, the Ministry approved the Aseng Plan of Development and first oil from the Aseng Field was produced in November 2011. In November 2007 Noble announced that the I-3 (Yolanda) exploration well was a dry gas discovery and in July 2008 announced that the I-6 (Diega) exploration well was another oil discovery in Block I. In December 2006 Santa Isabel Petroleum Company Ltd, a subsidiary of the China National Petroleum Corporation (CNPC) farmed-in and took over operatorship of Block M. In 2011 Santa Isabel withdrew from Block M and Fruitex resumed as operator.
In May 2006 the Ministry announced that two new PSCs had been signed. Block R, offshore Bioko Island was awarded to Ophir Energy and Block S, offshore Rio Muni was awarded to the China National Offshore Oil Corporation (CNOOC). In December 2006 Santa Isabel Petroleum Company Ltd, a subsidiary of the China National Petroleum Corporation (CNPC) farmed-in and took over operatorship of Block M. In 2011 Santa Isabel withdrew from Block M and Fruitex resumed as operator.
In 2007 ExxonMobil drilled the Langosta-1 gas condensate discovery in Block C and in May 2009 Repsol Exploration Guinea SA became the operator of Block C, following the withdrawal of ExxonMobil and SK Corporation from the licence. Block C was subsequently relinquished in 2012. In January 2009 Ophir Energy announced that the R-2 and R-3 exploration wells in Block R were gas discoveries and in October 2011 the Block R PSC was amended to include unlicensed acreage north-west of the original contract area. In return for the expansion of the acreage, Ophir has committed to accelerate exploration activity in the enlarged area through the drilling of 2 further commitment wells. These wells will form part of a proposed 3-4 well drilling programme which is planned to commence in 1H 2012.
In July 2009 a new PSC for Block X, in the Douala Basin, offshore Bioko Island was awarded to Starc Limited (operator) and Glencore Exploration (GE) Limited.
In early 2010 PetroSA drilled the Q-1 exploration well and in late 2010 acquired additional 3D seismic in Block Q. Also in January - April 2010 CNOOC drilled the unsuccessful S-1 and S-2 exploration wells in Block S.
In July 2010 two new PSCs were awarded to Gazprom Neft, Block T, offshore Bioko Island and Block U, offshore Rio Muni. Gazprom Neft will carry out geophysical and geological evaluation of the existing data and will drill at least one well in each block. Also in July 2010 new PSCs were awarded to Vanco Corisco Deep Ltd over Block K, offshore Rio Muni and Afex Global were awarded Block V, offshore Bioko Island. In September 2011 Glencore farmed-in to Block V and took over as operator.
In March 2011 a new PSC was awarded to Marathon Oil and SK Innovation Co., Ltd over Block D, offshore Bioko Island. In November 2011 Noble Energy announced that the Alen 1-G1 Pilot Well had encountered hydrocarbons in the Carla Prospect, Block O, Offshore Bioko Island, Equatorial Guinea. The Alen 1-G1 Pilot, designed as a gas injector well in the Alen Field Development, was deepened as a pilot hole to target the Carla Prospect which underlies the Alen Field, and encountered approximately 9.9 meters of net oil pay in the objective interval. The operator of Block O, Noble Energy, estimates that the discovered gross resources range between 35 and 100 million barrel oil equivalent of which 80 percent is liquids. Recent appraisal work at Diega, a 2008 discovery in Block I, has confirmed a gross resource range of 45 - 110 MMBoe with 60 percent liquids. Noble Energy anticipates developing both Carla and Diega through the infrastructure at Aseng. Both discoveries are expected to contribute production in 2015.
In July – September 2012 Ophir Energy announced that the R-4 (Tonel-1), the R-5 (Fortuna East-1) and R-6 (Fortuna West-1) wells were all gas discoveries, bringing the estimated proved and probable reserves for Block R to 2.9 TCF.
In June 2012 a new PSC was awarded to Marathon Oil and GEPetrol over Block A-12, offshore Bioko Island.
In December 2012, the Ministry announced the signature of 8 new PSC’s offshore Bioko Island and offshore Rio Muni. The 8 PSC’s were Block W (Offshore Rio Muni) awarded to Murphy Equatorial Guinea Oil Co. Ltd (operator)and Pan Atlantic Oil and Gas Ltd; Block Y (Offshore Rio Muni) awarded to Xuan Energy Limited (operator), Brenham Equatorial Guinea LLC, Strategic Oil & Gas Resources Ltd., and Royal Gate Energy Ltd; Block Z (Offshore Bioko Island) awarded to Royal Gate Energy Ltd (operator); Block EG-01 (Offshore Rio Muni) awarded to G3 Oleo e Gas (operator); Block EG-02 (Offshore Bioko Island) awarded to Pan Atlantic Oil and Gas Ltd. (operator, Novamark International and Atlas Petroleum; Blocks EG-03 & EG-04 (Onshore Rio Muni) awarded to Elegance Power (operator; and Block EG-05 (Offshore Bioko Island) awarded to Glencore Exploration and Production (EG) ltd (operator) and Pioneer Brass Ltd.