The Parnaíba Basin had been suspected of holding hydrocarbons since the late 1940s, when Brazil's National Petroleum Council drilled two early test wells. Between the 1960s and 1980s, Petrobras and a revolving cast of contractors kept surveying, but the basin was enormous - more than 600,000 square kilometers - and the data collected never felt conclusive. In June 2002, the newly formed National Agency of Petroleum, Natural Gas and Biofuels offered exploration blocks in the fourth federal bidding round. No one bought them. The basin looked too risky. It was not until September 2009 that anything changed, when OGX - the oil and gas arm of Eike Batista's EBX Group, then one of Brazil's most visible business empires - purchased a 70 percent stake in seven onshore blocks held by the smaller operator Petra Energia.

Drilling resumed on 5 July 2010. Five weeks later, on 12 August, OGX announced the discovery of natural gas reserves in well 1-OGX-16-MA in the PN-T-68 block. A second strike followed in the same well on 2 September. Two more discoveries came on 17 and 26 November in the OGX-22 well. A basin that had been written off was suddenly a producing field. OGX Maranhão expanded its position, buying half of an additional block in September 2011, and in September 2012 obtained the operating license it needed to produce the Gavião Azul (Blue Hawk) and Gavião Real (Royal Hawk) fields. Commercial gas began flowing in January 2013. Today, under Eneva's ownership, the Parnaíba Basin produces up to 8.4 million cubic meters of gas per day - about 4.4 percent of Brazil's total natural gas output.

The generating side grew in stages. Maranhão III won an A-3 auction held by the national electricity regulator ANEEL in August 2011, under the Parnaíba II name. Parnaíba I - actually a combination of what had started life as Maranhão IV and Maranhão V, each rated at 337.6 MW - was commissioned in the first months of 2013. Its first turbine synchronized to the national grid on 19 January for testing and received commercial authorization on 1 February. The second turbine came online 8 February, the third on 16 March, the fourth on 5 April. Parnaíba III (the MC2 Nova Venécia 2 plant) started commercial operation on 14 October 2013. Parnaíba IV followed on 13 December 2013. Parnaíba II came online on 1 July 2016, completing the initial four-plant complex. Two further expansions - Parnaíba V, a 386 MW combined-cycle unit that uses waste heat from Parnaíba I, and Parnaíba VI, a 92 MW expansion of Parnaíba III - have since pushed the complex toward 1.9 GW of total capacity.

Eneva's business model is unusual in the power industry, and it is the reason the Parnaíba Complex exists in this location. The company operates both the gas fields and the power plants, and it runs the plants as dispatchable capacity rather than baseload. That means the complex fires up when Brazil's hydro-dominated electricity grid needs backup - during dry years when reservoir levels fall, during peak evening demand, during supply emergencies - and throttles back when hydropower is abundant. Gas production follows the plants' demand rather than feeding a pipeline to distant consumers. The combined configuration keeps costs down: no long-distance gas transport, no separate marketing operation, no mismatch between what's drilled and what's burned. Eneva now holds a concession area of more than 40,000 square kilometers in the Parnaíba Basin and passed 100 drilled wells in 2017.

The five municipalities whose land and subsurface rights feed the complex - Lima Campos, Santo Antônio dos Lopes, Capinzal do Norte, Trizidela do Vale, and Pedreiras - were historically among the poorest in Maranhão. Royalty payments from gas production transformed their budgets. *Valor Econômico* ran a 2017 story titled *Gás "enriquece" cinco municípios pobres no MA* - "Gas enriches five poor municipalities in Maranhão" - documenting new schools, paved roads, and expanded health services funded by the revenue. Maranhão as a whole became the second-largest onshore gas producer in Brazil. Critics have pointed out that much of the wealth created by the complex flows out of the region to Eneva's shareholders and the national grid, not to the communities atop the gas reservoirs, and that is a fair critique of extractive industry everywhere. What the royalty system does provide is at least a portion. For towns that had almost nothing, a portion of something substantial is, for now, a meaningful change.