By Lucas Iberico Lozada

NEW YORK, Jan 6 (Reuters) - Pioneer Natural Resources , a major producer in the Permian Basin of West Texas, said on Tuesday it has restructured most of its 2015 hedge position to protect against further falls in oil prices.

The move reflects a growing belief in the industry that prices will not return to pre-crash levels this year, and is one of the more effective tools in U.S. producers' arsenal in their stare-down with OPEC over market share.

Pioneer's decision follows a Monday announcement by smaller rival Concho Resources that it would be dramatically scaling back its 2015 spending plan.

Pioneer said in a statement that it had replaced most of its options-based "three-way collars" with fixed-price swaps. This exchanges a system with more potential upside for one that offers greater protection on the way down, after it was left exposed in November.

Collars guarantee producers sales within a given range, provided the market price for a barrel of oil does not fall beneath a put option, set lower than the "floor" of the range. Swaps guarantee future sales at a fixed price but limit potential gains on the upside.

For its third quarter, Pioneer reported a robust hedge book, with collars in place for some 96,000 barrels per day (bpd), about 85 percent of what the company says it expects to produce in 2015. But those collars were set with the lower put option - which analysts call a "subfloor" - at $73.54 a barrel, leaving the company unprotected when prices dropped below $70 in late November.

By replacing the inert collars with swaps set at just above $71 per barrel for 82,000 barrels per day and leaving its 2016 collars in place, the company is effectively betting that prices will stay low throughout the year and rise again in early 2016.

The company did not respond to a request for comment on which lender was used for the transaction, and how much it had been charged.

(Reporting by Lucas Iberico Lozada; Editing by Richard Chang)