4. Oil and Gas Properties

The following tables set forth certain information with respect to our oil and gas producing activities (all within the United States) for the periods presented.

The following table sets forth the composition of exploration expenses for the years ended December 31:

	2012			2011		2010
Lease rental (income) expense	$	(68,205	)	$	—	$	70,839
Geological and geophysical	197,452			374,782		591,909
Settled asset retirement obligations	163,404			620,630		304,574
Total	$	292,651		$	995,412	$	967,322

The following table sets forth the composition of impairment and abandonment expenses for the years ended December 31:

	2012		2011		2010
Impairment and abandonment of proved properties	$	114,365,871	$	—	$	473,105
Impairment and abandonment of unproved properties	3,524,368		14,954,633		21,780,954
Total	$	117,890,239	$	14,954,633	$	22,254,059

2012 Asset Impairments. Non-cash impairments of proved properties include $114.4 million related to conventional gas assets in South Texas and unconventional gas assets in East Texas. See Note 5 - “Fair Value Measurements” for more details regarding the valuation methodology used to measure these impairments. Non-cash impairments of unproved properties include $3.0 million related to individually insignificant acreage.

2011 Asset Impairments. Non-cash impairments of unproved properties include $12.2 million related to our East Texas acreage expirations and $2.8 million related to individually insignificant acreage.

2010 Asset Impairments. Following a change in strategic focus from gas to oil-weighted opportunities, we re-allocated our future capital budget. As a result of this change in strategy, we incurred a $22.3 million non-cash impairment expense primarily related to our East Texas acreage.

The following table shows oil and gas property dispositions as of December 31:

	2012		2011		2010
Oil and gas properties	$	—	$	—	$	2,601,997
Accumulated depreciation, depletion, amortization and impairments	—		—		(1,406,066		)
Net oil and gas properties	$	—	$	—	$	1,195,931

The dispositions of assets resulted in a loss of zero, zero and $1.1 million for 2012, 2011 and 2010, respectively.

We have capitalized zero and $3.5 million, respectively, in exploratory well costs pending determination of proved reserves for periods less than one year at December 31, 2012 and 2011. We have not capitalized exploratory well costs for periods greater than one year at December 31, 2012 and 2011.