Mystery graph - what is the data?

Okay … here’s a graph of data I collected. The axes aren’t labeled (as you can see). What’s your guess? UPDATE (9/9/08): Silver Fox wins (RCfon gets credit for guessing price of oil, which helped) — the above graph shows gasoline prices in the San Francisco Bay Area from May 2007 until now. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Okay ... here's a graph of data I collected. The axes aren't labeled (as you can see).

What's your guess?

UPDATE (9/9/08): Silver Fox wins (RCfon gets credit for guessing price of oil, which helped) -- the above graph shows gasoline prices in the San Francisco Bay Area from May 2007 until now.

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