Exhibit 12a

UniSource Energy Corporation

Computation of Ratio of Earnings to Fixed Charges

	3 Months Ended		12 Months Ended		12 Months Ended
	March 31,		March 31,		December 31,		December 31,		December 31,		December 31,		December 31,
	2012		2012		2011		2010		2009		2008		2007
	- Thousands of Dollars -
Fixed Charges:
Interest on Long-Term Debt	$	19,135	$	74,260	$	73,217	$	65,020	$	58,134	$	70,227	$	73,095
Other Interest (1)		175		3,055		2,535		1,651		3,468		1,837		5,480
Interest on Capital Lease Obligations		9,120		42,862		44,874		52,540		53,682		57,272		64,499
Estimated Interest Portion of Rental Expense		206		900		926		240		345		188		258
Total Fixed Charges	$	28,636	$	121,077	$	121,552	$	119,451	$	115,629	$	129,524	$	143,332
Net Income	$	6,476	$	102,979	$	109,975	$	112,984	$	105,901	$	16,955	$	60,712
Add:
Losses from Equity Investees		—		—		—		5,570		1,834		713		340
Income Tax Expense		3,208		62,692		66,951		76,921		63,232		18,747		40,274
Total Fixed Charges		28,636		121,077		121,552		119,451		115,629		129,524		143,332
Total Earnings before Taxes and Fixed Charges	$	38,320	$	286,748	$	298,478	$	314,926	$	286,596	$	165,939	$	244,658
Ratio of Earnings to Fixed Charges		1.338		2.368		2.456		2.636		2.479		1.281		1.707

(1) Excludes recognition of Allowance for Borrowed Funds Used During Construction.