From Consumer Reports

Myth: Engine oil should be changed every 3,000 miles.

Reality: Although oil companies and quick-lube shops like to promote this idea, it's usually not necessary. Go by the recommended oil-change schedule in your vehicle's owner's manual. Most vehicles driven under normal conditions can go 7,500 miles or more between oil changes. Some models now come with a monitoring system that alerts the driver when the oil needs changing. Depending on driving conditions, these can extend change intervals to 10,000 or 15,000 miles.