The California Public Utilities Commission on Thursday approved a plan to allow Southern California Gas Company to spend $1 billion to replace nearly 6 million customer meters with new computerized “smart meters,” that would allow business and residential customers to better track their natural gas usage.

The meter replacement program will start in 2012 and is expected to take five years. It applies to all residential and commercial customers in the Gas Co.’s territory, which stretches from Visalia in the Central Valley south to the Mexican border. Southern California Gas Co. is a unit of San Diego-based Sempra Energy.

The new “smart meters” are similar to the meters now being deployed by the state’s electric utilities in that they track customer gas usage by the hour, allowing for more frequent updates. But unlike electric utilities, the Gas Co. has no plans to tier rates based on the time of day gas is used.

Instead, the biggest advantage for business customers will be the ability to track down problems in their operations that create spikes in natural gas consumption, according to Sempra spokesman Raul Gordillo. For example, in a laundromat, daily or hourly reports on gas consumption could allow operators to find out about a malfunctioning dryer much more quickly than with the current monthly bills.

In approving the smart meter program Thursday, the Public Utilities Commission made some changes to Southern California Gas Co.’s original plan, most notably requiring Sempra shareholders to share equally with ratepayers any cost overruns.