Mexico's Institutional Revolutionary Party (PRI) and its Green Party allies will have 241 of 500 seats in the lower house of Congress, one more than originally projected after the July 1 election, final results obtained by Reuters on Wednesday showed.

The PRI, the party of incoming President Enrique Pena Nieto, will still be short of an absolute majority, but the extra seat will make it marginally easier for the next administration to form alliances in support of its reform agenda.

If the PRI and the Greens were to team up with the New Alliance Party (PANAL), which will have 10 seats, they could garner a simple majority of 251 votes. PANAL had briefly sided with the PRI before the election campaign, but it is not certain how much support the party will give the new administration.

The seat was awarded by the electoral tribunal following disputes in regional ballots in a decision due to be announced publicly on Thursday, according to an electoral official who declined to be identified. In awarding the seat to the PRI, the tribunal took it away from an alliance of leftist parties.

The new Congress will assemble on September 1, while Pena Nieto is due to take office in December, replacing President Felipe Calderon.

Pena Nieto, who returned the PRI to power after 12 years in the wilderness when he won 38 percent of the vote in the July election, has promised to reform Mexico's fiscal, energy and labor laws.

Calderon's National Action Party, or PAN, will have 114 deputies in the new Congress and may also support reforms aimed at allowing more foreign investment in the oil industry and making it easier for employers to hire and fire workers.

Three leftist parties, who want to keep existing labor protections and national control of the oil industry, have the remaining 135 seats in the lower house.

In the upper house, the PRI and Green Party will be represented by 61 senators, followed by 38 for the PAN, 28 for the leftists and one for the New Alliance Party.

Leftist presidential candidate Andres Manuel Lopez Obrador, who came second in the vote, has filed a legal complaint accusing Pena Nieto of buying votes and over-spending in his campaign.

The electoral tribunal has to rule on the accusations before it can officially declare Pena Nieto as president elect, a decision due by September 6.