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 efforts 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 licences 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 were drilled without commercial success. Hamilton Oil Co. (subsequently BHP Petroleum) carried out seismic work in a Corisco Bay licence before withdrawing in 1995.

The Alba acreage was relicensed in 1990 to US independent Walter International who commenced production in 1991 from two new wells. In 1995 Nomeco (now CMS Oil and Gas) acquired Walter and they progressively expanded onshore processing capacity to cope with increased production from additional Alba wells. Other exploration in the Alba block has included North Alba-1 (Walter, 1992), South Luba-1 (CMS, 1996), and the Riaba-1 and East Luba-1 marginal discoveries (CMS, 1997). The success of the Estrella-1 well (CMS, 2001), a gas condensate discovery 6 km north of the Alba Field, has emphasised the large potential of the Alba Block. All CMS assets were acquired by Marathon in 2001 and they have continued with investment and expansion.

United Meridian Corporation (UMC, now Ocean Energy) licensed Bioko Blocks A and B in 1992, and blocks C and D in 1995 and drilled the Dorado-1 well in Block A. Mobil then farmed-in to Block B and drilled the Delta-1 well in Block B in 1994 and the Zafiro-1 discovery well in 1995. Mobil has drilled eight exploration wells in Block B outside of the Zafiro area, with small discoveries at Azurita-1 (1997), Berilo-1 (1998) and Turmelina-1 (1998). Mobil also farmed-in to Block C in 1999 and drilled the Ostra-1 exploration well, followed by Oreja Marina-1 exploration well in 2001 and the Estrella de Mar-1 exploration well in 2002. During 2000, Ocean Energy relinquished Block A and operatorship of Block D was taken over by CMS. Six exploration wells were drilled by Ocean in Block D and resulted in small discoveries at Tsavorita, Estaurolita, Apatito and Ambar (all in 1997). Since farming-in to Block D, CMS has drilled the Los Loros-1 exploration well (2001) and after the ownership change to Marathon, wells Agate-1 and Ibis-1 were drilled in 2002.

Elsewhere in the areas offshore Bioko, Elf signed a licence in 1999 for Block E, and drilled the Hippocampo-1 well before relinquishing the area.

Triton Energy was awarded Rio Muni Blocks F & G in 1997, covering areas previously licenced to Elf. 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 first production in November 2000. In response to 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 has resulted in 18 successful wells that have proved up several hundred million barrels of oil in northern Block G. Additionally the G-13 discovery was made in southern Block G in late 2002 which will be appraised in 2003.

Following the Deep Water Licensing Round of 1998-99, five exploration licences were signed during 2000 with Atlas Petroleum (Blocks H, I and J), Vanco (Block K) and Chevron (Block L) as operators. Extensive 3D seismic surveys were acquired in these licenses in 2001 and exploratory drilling will commence by early 2003.

During 2002 new exploration licences were awarded to Petronas for Block N covering Corisco bay and for the Fruitex Group covering Block M in western offshore Rio Muni.