FACTBOX: U.S. laws on gay marriage, civil unions

(Reuters) - The California Supreme Court ruled on Thursday the state cannot bar same-sex marriages, marking a major victory for gay rights advocates that may have national implications.

Here is a look at laws on gay marriage and same-sex civil unions in the United States:

* Massachusetts is the only U.S. state to allow gay marriage. Its highest court ruled in 2003 that a ban on gay marriage was unconstitutional, paving the way for America's first same-sex marriages the following year.

* Connecticut, New Hampshire, New Jersey and Vermont permit same-sex civil unions that grant largely the same state rights as married couples -- from insurance coverage to tax benefits and hospital visiting rights -- but lack the full, federal legal protections of marriage.

* California, Maine, the District of Columbia, Hawaii and Washington each offer gay couples some legal rights as partners.

* Currently, 45 states have laws explicitly prohibiting same-sex marriage, including 26 with constitutional amendments restricting marriage to one man and one woman and 19 with statutory laws barring same-sex unions.

* The patchwork of laws has caused some unusual complications. Rhode Island's top court, for example, ruled in December 2007 that a same-sex couple married in Massachusetts could not legally divorce in Rhode Island, saying the state's family court did not have authority over same-sex marriages.

* Massachusetts currently allows out-of-state same-sex couples from just two states -- Rhode Island and New Mexico -- to marry there, since those states' laws do not clearly prohibit gay marriage.

* More than 8,000 same-sex couples have married in Massachusetts.