As Uber and Lyft prepare to go public, both companies are reviving an old and costly tactic to boost market share: discounts.

Lyft, which is likely to be first to hit the public market, sharply ramped up discounts for riders in recent weeks, according to people close to both companies. The discounts covered as many as a third of its trips, according to an estimate gathered by Uber. The plan worked: Lyft’s share of the U.S. market, measured by revenue, has risen to around 34% from about 30%, according to Uber’s internal estimates. Uber has the rest of the market.