The following disaggregates our revenue by major sources for the three and six months ended March 31, 2020 and March 31, 2019:

	Three Months Ended March 31,				Six Months Ended March 31,
(in thousands)	2020		2019		2020		2019
Petroleum Products:
Home heating oil and propane	$	413,466	$	554,364	$	756,812	$	918,566
Other petroleum products		67,809		83,036		157,151		177,541
Total petroleum products		481,275		637,400		913,963		1,096,107
Installations and Services:
Equipment installations		20,158		20,384		50,723		50,367
Equipment maintenance service contracts		27,764		26,678		55,672		54,997
Billable call services		13,866		15,120		31,650		33,138
Total installations and services		61,788		62,182		138,045		138,502
Total Sales	$	543,063	$	699,582	$	1,052,008	$	1,234,609

We recognize an asset for incremental commission expenses paid to sales personnel in conjunction with obtaining new residential customer product and equipment maintenance service contracts. We defer these costs only when we have determined the commissions are, in fact, incremental and would not have been incurred absent the customer contract. Costs to obtain a contract are amortized and recorded ratably as delivery and branch expenses over the period representing the transfer of goods or services to which the assets relate. Costs to obtain new residential product and equipment maintenance service contracts are amortized as expense over the estimated customer relationship period of approximately five years. Deferred contract costs are classified as current or non-current within “Prepaid expenses and other current assets” and “Deferred charges and other assets, net,” respectively. At March 31, 2020 the amount of deferred contract costs included in “Prepaid expenses and other current assets” and “Deferred charges and other assets, net” was $3.5 million and $6.3 million, respectively. At September 30, 2019 the amount of deferred contract costs included in “Prepaid expenses and other current assets” and “Deferred charges and other assets, net” was $3.4 million and $5.9 million, respectively. During the six months ended March 31, 2020 and 2019 we recognized expense of $1.9 million each period associated with the amortization of deferred contract costs within “Delivery and branch expenses” in the Condensed Consolidated Statement of Operations.

The Company has contract liabilities for advanced payments received from customers for future oil deliveries (primarily amounts received from customers on “smart pay” budget payment plans in advance of oil deliveries) and obligations to service customers with equipment maintenance service contracts. Contract liabilities are recognized straight-line over the service contract period, generally one year or less. As of March 31, 2020 and September 30, 2019 the Company had contract liabilities of $97.2 million and $127.0 million, respectively. During the six months ended March 31, 2020 the Company recognized $95.7 million of revenue that was included in the September 30, 2019 contract liability balance. During the six months ended March 31, 2019 the Company recognized $90.3 million of revenue that was included in the September 30, 2018 contract liability balance.