4. Investments in Available-for-Sale Securities

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

	Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. federal agency securities	$	49,608	$	56	$	(629)	$	49,035
Municipal securities		844,796		1,873		(552)		846,117
Certificates of deposit		1,542,914		8,482		(30,014)		1,521,382
Corporate debt securities		187,645		438		(8,545)		179,538
	$	2,624,963	$	10,849	$	(39,740)	$	2,596,072

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 gain of $14,118 and a net realized loss of $1,141 for the six months ended June 30, 2013 and 2012, respectively. The Company’s investment portfolio had a net realized gain of $25,104 and $660 for the three months ended June 30, 2013 and 2012, respectively.

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

	Cost		Fair Value
Due within one year	$	798,269	$	776,053
Due after one year through three years		751,955		752,081
Due after three years		1,074,739		1,067,938
	$	2,624,963	$	2,596,072

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.