A US federal judge struck down Oklahoma's ban on gay marriage, saying it was unconstitutional, close after a similar move in Utah that left gay couples rejoicing.
The ruling in the long-running case also followed a landmark Supreme Court decision in June finding that couples in same-sex marriages were entitled to the same benefits and protections as their heterosexual counterparts.
"The court holds that OkOlahoma's constitutional amendment limiting marriage to opposite-sex couples violates the Equal Protection Clause of the Fourteenth Amendment to the US Constitution," US District Judge Terence Kern wrote in his opinion.
A month ago, a federal judge in Utah overturned that state's ban on same-sex marriage, a decision that saw hundreds of couples get married.
But the US Supreme Court later temporarily blocked the weddings after the state filed an emergency request to stay the judge's ruling, though the federal government has said it would give full backing to about 1,300 gay marriages that took place between the two rulings.
Last month, the New Mexico state Supreme Court also declared same-sex marriage constitutional.
Kern said his ruling would not go into effect immediately, saying he would wait for the Utah case to go through the appeals process in the wake of the Supreme Court's decision to grant a stay.
So Oklahoma will not see same-sex marriages until Kern's decision goes into effect. And the state is likely to appeal, adding uncertainty to the fate of gay couples there.
In his ruling, Kern denounced the state's gay-marriage ban as an "arbitrary, irrational exclusion of just one class of Oklahoma citizens from a governmental benefit."
Gay rights activities hailed Kern's decision.
"With last year's historic victories at the Supreme Court guiding the way, it is clear that we are on a path to full and equal citizenship for all lesbian, gay, bisexual and transgender Americans," Human Rights Campaign president Chad Griffin said in a statement.
"Today's news from Oklahoma shows that time has come for fairness and dignity to reach every American in all 50 states."
Two plaintiff couples, Mary Bishop and Sharon Baldwin and Gay Phillips and Susan Barton, had filed their case in November 2004 a day after Oklahoma voters passed a constitutional amendment limiting marriage to a union between one man and one woman.