2012 ppg annual report and form 10-k 27 operations in 2011 compared to 2010 , but the increase was reduced by cash used to fund an increase in working capital of $ 212 million driven by our sales growth in 2011 . operating working capital is a subset of total working capital and represents ( 1 ) trade receivables-net of the allowance for doubtful accounts , plus ( 2 ) inventories on a first- in , first-out ( 201cfifo 201d ) basis , less ( 3 ) trade creditors 2019 liabilities