Are DVDs encoded in PAL or NTSC depending on the market they are intended for?

Basically would a region free DVD disc (made in Europe to play in europe) play on a US player on an NTSC TV?

They're not made for PAL or NTSC but the frame rate and number of lines is different according to where they are intended to be played - 50 Hz 576 lines for Europe, 60 Hz 480 lines for US.

Your player/TV needs to be able to handle the different frame rate, generally UK ones will handle 60 Hz ok but I'm not sure about the other way round.