7. Revenue

We disaggregate revenue from contracts with customers into three revenue categories: (i) product revenues, (ii) rental revenues and (iii) field service and other revenues. We have predominately domestic operations, with a small amount of sales being generated in Australia. For the year ended December 31, 2019, we derived 57% of our total revenues from the sale of our products, 22% of our total revenues from rental and 21% of our total revenues from field service and other. This compares to 53% of our total revenues from the sale of our products, 25% of our total revenues from rental and 22% of our total revenues from field service and other for the year ended December 31, 2018. In 2017, we derived 55% of our total revenues from the sale of our products, 23% from rental and 22% from field service and other. The following table presents our revenues disaggregated by category:


	Year Ended December 31,
	2019		2018		2017
Product revenue	$	357,087	$	290,496	$	189,091
Rental revenue		141,816		133,418		77,469
Field service and other revenue		129,511		120,221		74,631
Total revenue	$	628,414	$	544,135	$	341,191

At December 31, 2019, we had a deferred revenue balance of $1.4 million compared to the December 31, 2018 balance of $1.1 million included in accrued expenses and other current liabilities in the consolidated balance sheets. Deferred revenue represents our obligation to transfer products or perform services to a customer for which we have received cash or billed in advance. The revenue that has been deferred will be recognized upon product delivery or as services are performed. As of December 31, 2019, we did not have any contracts with an original length of greater than a year from which revenue is expected to be recognized in the future related to performance obligations that are unsatisfied.