Moody's Investors Service changed its ratings outlook on Atmos Energy Corp. to "positive" from "stable" on Friday, citing the natural gas company's rate increases.

The long-term "Baa2" senior unsecured rating was affirmed for the Dallas-based company.

In a note to investors, Moody's analyst Mihoko Manabe wrote that rate increases have helped Atmos deliver stronger results in the past year. Additional increases on deck for 2010 could help result in a one-notch upgrade from Moody's, Manabe said.

So far this year, Atmos has been approved for $20 million in rate increases. It was approved for $54 million last year.

Atmos also recently said it will make no further investments in its nascent midstream business, Manabe noted. The diversification into a riskier business line had been a concern for the ratings agency.

Shares of Atmos closed down 7 cents to $28.95 on Friday.