  CALGARY, Alberta Tue Apr 2, 2013 7:43pm EDT  Emergency crews
work to clean up an oil spill near Interstate 40 in Mayflower,
Arkansas March 31, 2013. REUTERS/Jacob Slaton   Credit:
Reuters/Jacob Slaton      So even as environmentalists seized on
oil spills last week in Arkansas and Minnesota to warn about the
impact of expansion in the tar sands -- the world's third-
largest crude deposit -- it appears only a crash in the price of
oil or unexpected regulation will derail the growing energy
interdependence.  "Short-term, this is not good for producers,
it's not good for Canadian oil going south, it's not good for
Keystone," John Stephenson, vice-president and portfolio manager
at First Asset Investment Management in Toronto said of the two
spills.    That may trump increasingly bad PR for Canada's oil,
much of which is produced by energy- and carbon-intensive
methods such as mining or steaming, making it a prime target in
the battle over policies to fight global warming.    In fact,
the two types of crude comp