Lyft’s share of the ride-hailing market has hit record levels in nearly 30 major U.S. cities in the past month, by dollars spent, according to new data. In the top 10 markets, Lyft’s highest share is 39.5% in San Francisco, and 33.5% in Los Angeles, according to Second Measure, which tracks credit card transactions.

Overall, Lyft has between 20% to 30% of the U.S. market, depending on who is counting, to Uber’s 70% to 80%. But the data show that Lyft has become a growing problem for Uber in some major cities, which could limit Uber’s ability to turn profitable. The U.S. is the world’s top market in terms of revenue per rider, and ride fares could reach more than $10 billion this year. Without profits in the U.S., Uber may not be able to continue investing in developing markets, such as India, Latin America and Southeast Asia. (The chart above shows Lyft’s market gains in 49 cities: Click on the year at the top of the chart to see the market share for that period.)