does postgresql backup require additional space on disk

[Julie Nishimura]

Hello,
we are almost out of disk space on one of our servers (99% full). If we run 
pg_dump to a diff location, does it require any additional disk space on our 
current server? I am asking, because on some other software, a backup might 
open transaction which keeps growing and eventually consume all space, keeping 
tran open for the backup duration. Please clarify? Thanks