Warren spent more than $1 million on payroll in the first quarter of 2019, more than double that of rivals such as US Senators Bernie Sanders and Kamala Harris, the two who raised the most money in the first quarter.
The total does not include other payroll-related expenses. She spent about $566,000 on payroll taxes and $114,000 on health insurance.
Warren has said she intends to build a "grassroots" campaign. She has sworn off expensive fundraisers and is relying almost entirely on online donations to fund her campaign.
Building a large campaign staff can create challenges. If a campaign begins to run short on cash, it is often more difficult to cut back on staff compared to trimming other expenses, such as advertising.