Google is offering a service-level agreement for a version of Google Apps, a move that may provide some comfort to enterprises spooked by a long Gmail outage and a buggy Apps portal earlier this month.

The Premier Edition of the Google Apps online productivity and collaboration suite will come with a 99.9 percent per-month uptime guarantee for the Gmail, Calendar, Docs, Sites and Google Talk services.

In effect, Google is promising compensation if downtime exceeds around 45 minutes a month -- but it won't count outages of less than 10 minutes' duration towards this total. The SLA conditions define downtime as when the "user error rate" exceeds 5 percent, as measured on the server side. Customers could therefore experience far more than 45 minutes of downtime, in shorter bursts, without compensation.

There'll be no compensation either if the downtime is for scheduled maintenance for which Google has given more than five days' advance notice. Scheduled downtime will not exceed 12 hours a year, Google said.

If Google doesn't hit its marks, it will give customers credit toward more service. For only 99 percent uptime, Google will add three days of service to the end of a contract; from 95 to 99 percent, seven days and for less than 95 percent, 15 days. The agreement says money can't be substituted for user credits.

The SLA may give Apps customer additional confidence in Google, which experienced several problems with its services this month.

The starting portal page of Google's Apps suite malfunctioned as the company was apparently updating the layout and other functions. Administrators complained they would have preferred it if Google warned them before making changes.

Some Google Apps customers could not access Gmail for up to 30 hours after a service outage earlier this month. Google already offers a 99.9 percent uptime guarantee for Gmail for users on Google Apps Premier. In user forums, system administrators complained of outraged CEOs and executives in their companies who could not access e-mail.

With its Apps, suite Google is trying to draw customers away from desktop-based software from companies such as Microsoft. While hosted software requires less maintenance and enables easier software updates, it also leaves in-house IT specialists with few options but waiting when things go bad.