The Human Rights Campaign has released its annual rankings of US companies by the support they give to LGBT employees, and revealed that nearly a quarter of the 850 companies surveyed scored full marks.

The Corporate Equality Index measures how LGBT-friendly employers are by examining insurance and benefits policies for current employees, recruitment policies for new employees and retention rates for LGBT staff.

Nearly half the US states do not have laws prohibiting discrimination in the workplace on the grounds of sexual orientation.

Race, gender, religion, national origin or disability discrimination are prohibited at the federal level.

193 of the 850 surveyed organisations met all the criteria necessary for a top score, an increase from only 13 who did so in 2001.

Half of the top 20 companies, by revenue, scored full marks: AT&T, Chevron, Ford, JP Morgan Chase, Bank of America, Hewlett Packard, Citigroup, Cardinal Health, Wells Fargo and IBM.

Joe Solmonese, president of the Human Rights Campaign said: “Corporate America is leading the charge for equality in the workplace.

“We commend the businesses that participated in the CEI. They understand that LGBT-inclusive workplace policies are the right thing to do and good business practices.”

The full text of the Corporate Equality Index 2012 can be found on the Human Rights Campaign website.