Was Dec 05 unusually cold in your location? The resources available at weather.com can help determine the answer to that question. Did your utility company raise the price of fuel?

I live in Fairfax, Va about 15 miles west of Wash DC. The 2-story (2400sf) and unfinished basement (1200sf) house was built in 1981. Temperatrue is set at 68 during the day and 62 overnight. Gas heat and hot water - family of four. i.e. 4 showers/day and laundry. Electricity used for cooking. Dec 05 gas bill was $214. Gas bill monthly average for 2005 was $100.
regards,
Mark