oil consumption puzzler

["Shaun D. Mullen" <smullen@philly.infi.net>]

The rate and manner in which my '92 100CSQW is consuming oil is puzzling
to this novice.  The vehicle is closing in on 200K and is beginning to
go through some oil, certainly a manageable amount at this point. 
Here's what's puzzling: The V6 is consuming some oil on my usual grind
-- 100 mile daily commute, about 700-800 miles a week of stop-and-go
local and freeway driving -- but is consuming practically no oil at all
on long drives such as a 550-mile, one-stop trip yesterday through
tidewater flats, hills and some low mountains.  What explains this? 
(Incidentally, gas mileage on the longer jaunts is spectacular,
averaging 25-27mpg.)

Shaun Mullen
West Grove, PA