What is the factory not dealer recommended mileage between oil changes on a 1993 Buick Skylark?

On a car that is 14 years old, the factory nor dealer recommendation is mute. If you use normal Oil and not Synthetic and do lots of city driving, stop and go, short trips, change it every 3,000 miles. If you do mostly highway driving, change it every 4,000 miles. If you use synthetic then change it every 5,000 miles. Where you live and the temperature is also a factor. If you live in a high heat area, then change it every 3,000 miles city/highway. Synthetic, every 4,000. Also be sure to replace the air filter every 30,000 miles and 15,000 in an extremely dusty area.