4. Investments in Available-for-Sale Securities

The following is a summary of the Company’s investment in available-for-sale securities as of September 30, 2013:

	Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. federal agency securities	$	90,778	$	129	$	(339)	$	90,568
Municipal securities		722,321		2,506		(659)		724,168
Certificates of deposit		1,567,570		12,821		(12,821)		1,567,570
Corporate debt securities		208,428		426		(9,892)		198,962
	$	2,589,097	$	15,882	$	(23,711)	$	2,581,268

The following is a summary of the Company’s investment in available-for-sale securities as of December 31, 2012:

	Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. federal agency securities	$	19,592	$	196	$	-	$	19,788
Municipal securities		1,154,841		2,882		(2,090)		1,155,633
Certificates of deposit		1,193,494		8,734		(16,904)		1,185,324
Corporate debt securities		285,524		4,164		(9,633)		280,055
Equity securities – ClearSign common stock		7,905		9,485		-		17,390
	$	2,661,356	$	25,461	$	(28,627)	$	2,658,190

The Company’s investment portfolio had a net realized loss of $3,419 and $1,231 for the nine months ended September 30, 2013 and 2012, respectively. The Company’s investment portfolio had a net realized loss of $14,511 and $89 for the three months ended September 30, 2013 and 2012, respectively.

The cost and fair value of investments in available-for-sale securities, by contractual maturity, as of September 30, 2013, were as follows:

	Cost		Fair Value
Due within one year	$	528,115	$	526,184
Due after one year through three years		1,045,080		1,042,919
Due after three years		1,015,902		1,012,165
	$	2,589,097	$	2,581,268

Expected maturities will differ from contractual maturities because the issuers of certain debt securities have the right to call or prepay their obligations without any penalties. Accordingly, the Company has classified the entire fair value of its investments in available-for-sale securities as current assets in the accompanying balance sheets.