When your company already generates billions in revenue, growing at double or even triple-digits is no easy task. The fast-growing behemoths below all have managed to do it. From pet care to pharmacy benefits to transportation and logistics firms--and yes, to Uber, too--here are the businesses with the most revenue on Inc.'s list of the fastest-growing, private U.S. companies in 2019.

10. Transportation Insight

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2019 Inc. 5000 rank No. 3596 | Three-year growth 97.27% | 2018 revenue $2.29B

The Hickory, North Carolina-based logistics business helps more than 1,500 manufacturers, retailers, and distributors optimize and manage their supply chains. With a network of 150 warehouses across North America, coupled with domestic and international shipping services, this 12-time Inc. 5000 honoree says it can help you reduce cycle times and improve customer satisfaction. That 97 percent three-year revenue growth was spearheaded by CEO Rennie Faulkner, along with Paul Thompson, Transportation Insight's founder and current chairman.

9. SRS Distribution

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2019 Inc. 5000 rank No. 3915 | Three-year growth 84.37% | 2018 revenue $2.6B

The business of building--or rebuilding--in America isn't slowing down. Since its founding in 2008, this wholesale roofing-products distributor based in McKinney, Texas, has followed a growth-by-acquisition strategy. In the past decade, it has acquired nearly 60 companies--eight of them in 2018 alone. Led by CEO Dan Tinker since 2017, the six-time Inc. 5000 honoree opened 23 new locations and increased same-store sales by more than five percent last year. Currently, it operates more than 250 locations in 43 states.

8. Chewy

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2019 Inc. 5000 rank No. 605 | Three-year growth 735.54% | 2018 revenue $3.5B

For those who argue that Pets.com--a casualty of the dot-com era--was ahead of its time, Chewy is clear evidence you're right. The eight-year-old e-commerce business that sells everything from dog and cat food to kitty litter and prescription drugs was snapped up by PetSmart for $3.5 billion in 2017. Its new owner took the company public in June at a valuation of $8.7 billion. While the Dania Beach, Florida, company was still private, however, it handily made Inc.'s list of the fastest-growing companies in America, with eye-popping 2018 revenue of $3.5 billion. 

7. Total Quality Logistics

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2019 Inc. 5000 rank No. 4609 | Three-year growth 62.65% | 2018 revenue $3.6B

After getting its start moving loads for the produce industry, the business CEO Ken Oaks started in 1997 has transformed into a freight brokerage empire. The company helps connect transportation providers like New Penn Motor Express and Estes Express Lines with sellers from industries including consumer goods and energy and infrastructure. The Cincinnati company helps move more than 7,400 different types of goods and employs over 5,500 people. It has made the Inc. 5000 list 14 times.

6. 84 Lumber Company

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2019 Inc. 5000 rank No. 4927 | Three-year growth 54.4% | 2018 revenue $3.8B

Named after its hometown--Eighty Four, Pennsylvania--the family-owned building supplies and materials business operates more than 250 stores across the U.S. Joe Hardy founded the company in 1956, and his daughter, Maggie Hardy Knox, has led the business since 1992. The company serves more than 100,000 customers and employs more than 5,500 people. It has also expanded to offer design services. Since 2011, it has rolled out kitchen and bathroom design studios in more than 30 stores.

5. CoAdvantage

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2019 Inc. 5000 rank No. 3847 | Three-year growth 89.17% | 2018 revenue $4.5B

The Tampa, Florida-based payroll and benefits provider knows a thing or two about how to handle money. Led by CEO Clinton Burgess, the HR company currently covers more than 90,000 worksite employees for clients ranging from small businesses and franchises such as Jersey Mike's and Domino's to nonprofit organizations like the Humane Society and the Boys & Girls Club. This is its fourth time on the Inc. 5000.

4. Carahsoft Technology

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2019 Inc. 5000 rank No. 3772 | Three-year growth 86.52% | 2018 revenue $5.3B

The suburbs of Washington, D.C., are awash in government contractors and subcontractors alike, but few can claim multibillions in revenue like Carahsoft Technology. The Reston, Virginia-based technology and IT services provider helps connect federal agencies including the U.S. Army, the Department of Homeland Security, and the U.S. Department of Agriculture with products from technology vendors such as SAP, Salesforce, Google Cloud, Amazon Web Services, and Dell. In the past three years, the company has grown its headcount to more than 1,000 people, up from 538 in 2015. Since its founding in 2004 by CEO Craig Abod, Carahsoft has landed on the Inc. 5000 12 times.  

3. Allied Universal

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2019 Inc. 5000 rank No. 1617 | Three-year growth 255.19% | 2018 revenue $5.8B

Like elevator company Otis and food service giant Aramark, Allied Universal is the kind of company you interact with on a daily basis but rarely realize it. Founded in 1957, the Santa Ana, California-based security and janitorial service provider caters to businesses across North America, with clients ranging from Amazon to Simon Malls, the largest mall operator in the U.S. Its more than 200,000 employees help protect and service more than 42,000 client sites on a daily basis. Led by CEO Steve Jones since 2016, Allied has made the Inc. 5000 list 10 times.

2. Uber

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2019 Inc. 5000 rank No. 913 | Three-year growth 464.91% | 2018 revenue $11.27B

Prior to going public in May at a valuation of $82 billion, the San Francisco-based ride hailing service wasn't just one of the fastest-growing private companies in America, it also was one of its biggest revenue drivers. In 2018, it booked $11.27 billion. In the decade since it was founded by Travis Kalanick and Garrett Camp, the company has expanded to 65 countries, offering services that include food delivery and freight transportation. While it has hit several roadblocks, including Kalanick stepping down as CEO in 2017 amid a string of scandals, the company is no less formidable. Current CEO Dara Khosrowshahi is betting a redesigned app and a new suite of subscription products will bring the company closer to profitability. 

1. Prime Therapeutics

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2019 Inc. 5000 rank No. 1073 | Three-year growth 390.57% | 2018 revenue $21.36B

Not even Uber can top Prime Therapeutics. Frankly, it doesn't even come close. Founded in 1998 to provide pharmacy services to several nonprofit health insurance providers, known as Blue Plans, the Eagan, Minnesota-based pharmacy and benefits manager has grown to serve more than 28 million members through its partnerships with health plan providers, employers, and government programs including Medicare and Medicaid. In 2017, it inked a key partnership with Walgreens to manage several of its specialty pharmacy operations and home delivery services. The company, which marks its eighth time on the Inc. 5000, has more than 3,300 employees. In April, it hired Ken Paulus as CEO.