How often do I need to change oil?

I moved to the Washington, DC area and now take public transportation to work and play. I’d been here ten months when I realized I hadn’t even put 3,000 miles on my car and hadn’t had an oil change. Since mileage can’t be an indicator, how often should I get an oil change to keep my '94 Tercel in shape to continue to give me 30 mpg?

Change your dino oil every three to four months,don’t rely on oil changes to preserve your mpg.

3-6 months or 3k whichever comes first should be suitable. Like oldschool said, keeping up on the car’s tuneups will help keep your mpg up not just oil changes.

It depends on how you accumulate those miles. Short trips in city traffic are hard on oil. Long trips on the highway are easy. An extreme example of the former would be a senior citizen who drives 5 miles to the senior citizens center every morning and 5 miles back home every evening. An extreme example of the latter would be a college student who lives on campus and only uses the car for a 300 mile round trip home once a month. Even though they both drive the same distance per month, the senior needs an oil change every three months while the student could safely go a year between changes.

In spite of mileage at minimum my preference is a spring and fall minimum oil change.

If I owned a 14 year old car that I didn’t drive much, I’d assess the oil change interval with the overall expectation for how long I planned to keep the car.
If you’re only going to keep it for another couple of years, then changing the oil every few months may be an overkill. If you plan to keep it longer, then following the time intervals in your owner’s manual may be more appropriate.

My 12 year old Plymouth Voyager has a great engine at 175K, but the body cancer is so bad that it will rust itself to the graveyard long before the engine dies.

What does the manual say? If no manual, I’d change it every 6k or 6 months, whichever came first.

Isn’t this covered in your owner’s manual?