Peace Now says Jewish population growth is three times higher in the area occupied in 1967 than in Israel itself.
It says settlers are bypassing a ban on using caravans to expand settlements by erecting pre-fabricated homes on site.
Israeli settlements in the occupied territories are deemed illegal under international law.
Israel had pledged to stop their construction as part of internationally-backed peace efforts.
Peace Now says there is continuing construction in 88 out of about 150 of the authorised settlements, in addition to the building of permanent structures in 34 unauthorised settlement outposts.
Settler leaders expressed pleasure about Peace Now's report, thanking it for "documenting their endeavour".
Peace Now's Director-General Yariv Oppenheimer said the Israeli military had stopped monitoring construction at the illegal outposts.
"There is no connection between what is happening in political negotiations and what is happening on the ground," he told Israeli Army Radio.
He accused Israel's political leaders of violating their commitments ahead of an international peace conference aimed at restarting negotiations with the Palestinians and hoping to set up a Palestinian state in the West Bank and Gaza Strip.
Analysts say the chances of success at the US-sponsored Annapolis conference are limited by Israeli settlement activity, as well as major concerns over security and institution-building on the Palestinian side.
Peace Now's report says most of the construction is in large settlement blocs located on the west side of the barrier Israel is building in the West Bank.
It said natural increase and the relocation of ultra-Orthodox families to settlements had led to the three-times higher population growth compared with in Israel.
A source in the Yesha council which represents the Jewish settlement movement said Peace Now's findings proved it had achieved an unstoppable momentum.
© 2007 BBC News