Throughout Puerto Rico, the fares for taxis are typically quoted on a flat-rate basis, based on time and distance. You should be quoted, in advance, the exact fare for your trip. Taxis Turisticos (white taxi-cabs that display a sentry box logo) are endorsed by the Puerto Rico Tourism Company and offer reliable service. These taxis all offer flat rates. Some taxis that are privately owned and operated, however, rely on meters to calculate fares.
If you're staying at a resort and want to tour the island or visit a specific tourist attraction at your own pace, an alternative to renting a car is to hire a taxi for a half or full day. Rates for this can be negotiated with a cab driver directly or arranged through your resort. This will be more expensive than renting a car, but you'll benefit from having a private tour guide, plus someone who will do the driving for you and who won't get lost.