I would be curious to know what the industry average is of ExxonMobile. Usually 30 days to collect money owed from customers is not a bad ratio and is common with many businesses. Once that ratio starts to creep in past 35, 40, 45 days, then the company could be in trouble with their cash flow and steer investors away from investing in them. It is import for companies to be able to collect the cash as soon as they can so they have it on hand and are able to use that cash for other purchases or investments.