General Nature of Business Clean Energy Fuels Corp., together with its majority and wholly owned subsidiaries (hereinafter collectively referred to as the Company, unless the context or the use of the term indicates or requires otherwise) is engaged in the business of selling natural gas as an alternative fuel for vehicle fleets and related natural gas fueling solutions to its customers, primarily in the United States and Canada. The Companys principal business is supplying renewable natural gas (RNG), compressed natural gas (CNG) and liquefied natural gas (LNG) (RNG can be delivered in the form of CNG or LNG) for light, medium and heavy-duty vehicles and providing operation and maintenance (O&amp;M) services for public and private vehicle fleet customer stations. As a comprehensive solution provider, the Company also designs, builds, operates and maintains fueling stations; sells and services natural gas fueling compressors and other equipment used in CNG stations and LNG stations; offers assessment, design and modification solutions to provide operators with code-compliant service and maintenance facilities for natural gas vehicle fleets; transports and sells CNG and LNG via virtual natural gas pipelines and interconnects; procures and sells RNG; sells tradable credits it generates by selling RNG and conventional natural gas as a vehicle fuel, including Renewable Identification Numbers (RIN Credits or RINs) under the federal Renewable Fuel Standard Phase 2 and credits under the California and the Oregon Low Carbon Fuel Standards (collectively, LCFS Credits); helps its customers acquire and finance natural gas vehicles; and obtains federal, state and local credits, grants and incentives. In addition, for all periods presented before March 31, 2017, the Company produced RNG at its own production facilities, and for all periods presented before December 29, 2017, the Company manufactured natural gas fueling compressors and other equipment used in CNG stations. See Notes 4 and 5 for more information. Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to state fairly the Companys consolidated financial position as of September 30, 2018 , and results of operations and comprehensive loss for the three and nine months ended September 30, 2017 and 2018 , and cash flows for the nine months ended September 30, 2017 and 2018 . All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and nine month periods ended September 30, 2017 and 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other interim period or for any future year. Certain information and disclosures normally included in the notes to consolidated financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (the SEC), but the resultant disclosures contained herein are in accordance with accounting principles generally accepted in the United States of America (US GAAP) as they apply to interim reporting. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2017 that are included in the Companys Annual Report on Form 10-K filed with the SEC on March 13, 2018. Reclassifications During the nine months ended September 30, 2018 , the Company adopted Accounting Standards Update (ASU) No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (see Note 20 ). The new standard requires restricted cash and restricted cash equivalents to be included as components of total cash and cash equivalents as presented on the statement of cash flows. As a result, the Company chose to also conform this classification on the accompanying condensed consolidated balance sheets. This resulted in prior period restricted cash of $1,127 as of December 31, 2017 being reclassified into one line item with cash and cash equivalents to conform to presentation as of September 30, 2018 . In addition, certain prior period amounts have been reclassified in the condensed consolidated statements of cash flows to conform to the current period presentation. These reclassifications had no material impact on the Companys consolidated financial position, results of operations, or cash flows as previously reported. Use of Estimates The preparation of condensed consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying condensed consolidated financial statements and these notes. Actual results could differ from those estimates and may result in material effects on the Companys operating results and financial position. Significant estimates made in preparing the accompanying condensed consolidated financial statements include (but are not limited to) those related to revenue recognition, goodwill and long-lived asset impairment assessments, income tax valuations and fair value measurements.