Calculating the cost of ethylene is not straight forward. You need to calculate the co-products made with the ethylene and credit them to the cost calculation. For this, you need the yield pattern for the cracker. ICIS runs a training courses and the The Next Level course (which follows the Beginner's course) run in Europe and the US devotes nearly half a day to the cost of production and profitability including an exercise that involves calculating an ethylene margin. The link below gives more details: http://www.icistrainingsite.com/p/2757