EXHIBIT 12

COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2006		2005		2006		2005
	(Thousands of dollars, except ratio amounts)
Income before income taxes	$	105,708	$	101,614	$	201,121	$	192,563
Share of undistributed losses from 50%-or-less-owned affiliates, excluding affiliates with guaranteed debt		128		1,199		816		2,334
Amortization of capitalized interest		328		322		650		644
Interest expense		12,718		13,860		25,783		26,534
Interest portion of rental expense		1,326		722		1,726		1,391
Earnings	$	120,208	$	117,717	$	230,096	$	223,466
Interest	$	13,659	$	13,991	$	26,925	$	26,776
Interest portion of rental expense		1,326		722		1,726		1,391
Interest expense relating to guaranteed debt of 50%-or-less-owned affiliates		—		—		—		—
Fixed Charges	$	14,985	$	14,713	$	28,651	$	28,167
Ratio of Earnings to Fixed Charges		8.02		8.00		8.03		7.93