Car will start but then sputters off like it's not getting enough power to stay running

Car started but then sputtered & shut off. Did this quite a few times. I pressed accelerator to raise rpm but then rpm slowly came down, sputtered & then shut off. I put in reverse, it moved a little then same thing, sputtered & shut off. Recently it has sputtered while driving but the sputtering stopped after a few seconds without shutting off. Battery is fairly new (not even 2 yrs old). It just seems it's not getting enough power to keep car running. What could be the problem??