At minimum, you get $4 per delivery. But the final payout is based on the distance you traveled to make the delivery. That’s why a car is the preferred delivery method for couriers who work Postmates, though bikers also can do well. Walkers can have an advantage in that it’s possible to do more deliveries per hour in a certain area. Postmates will determine which jobs to send your way depending on your transportation mode, though I found out the hard way the system is not always perfect.
Source: Inside the mobile-only, on-demand market (and gig economy), Part I | Mobile Payments Today