The first half-hour after you pick up a bike is always free, with an extra euro tacked on for the first additional half-hour, two euros for the second and four euros for every extra half-hour from then on.

The sliding price scale, conceived to keep the bikes in rotation, means that if you want to spend a leisurely day riding through the gardens of the Bois de Boulogne, it would be cheaper to rent a bike from a shop.

But if you want to stop at the Louvre, then head to the boutiques of the Saint Germain neighborhood for some shopping, then crash at your hotel in eastern Paris — with the flexibility to take a bus or the Metro instead if you're tired — then Velib' is your best bet.

The bikes themselves, however, are rather utilitarian — three-speed touring bikes, weighing nearly 50 pounds each.

Here's how the program works:

Stop in at any station around town with your credit card. They accept American Express, Visa and MasterCard, among others.

Each station comes with an electronic vending machine with instructions in eight languages. Select "English," and the machine will walk you through the instructions. Along the way, you must authorize Velib' to deduct $205 from your card if the bike is not returned within 24 hours. (For a one-year subscription, you have to sign up online or by mail to use the service, but for a one- or seven-day pass, you can do it at the machine.)

Once you've picked a bike, you have 60 seconds to push a button on the stand and pull the bike free. Adjust the seat, and you're ready to go. The bike has a basket and a built-in lock, so you can secure it if you need to run into a shop or make a quick stop. For longer stops, you'll save money if you return the bike to a station.

To put the bike back, you slide it into the stand, and you'll hear a beep and see a blinking light if it's attached right. Be sure to push it in firmly.

One drawback for the tourist: Since the stations are not manned, there's no one to ask for help with directions, so bring a map and be prepared to stop a passer-by if you get lost.

On my test ride, I did a reconnaissance mission for what I would consider the perfect summer afternoon-into-evening, when the sun stays out until after 10 p.m.

The itinerary: Pick up a bike near your hotel and head to the Palais Royal gardens, a quiet rose-filled square in the middle of town, for a coffee or a stroll. From there, head by foot to nearby rue Montorgueil, a market street where you can buy cheese, baguettes and a bottle of wine. Grab a bike at the rue des Petits Carreaux station and park it at the Pont Saint Louis station near the Seine, and look for a spot on the quays for your picnic blanket.