At least four automakers — Toyota, Volkswagen, Fiat Chrysler and Mitsubishi — continue to sell new vehicles with defective Takata air bags that will need to be recalled, according to a Senate Commerce Committee report released Wednesday.

The report underscores the convoluted way in which the mass recalls of Takata air bags have unfolded, with new models still being fitted with defective air bags and, in some cases, recalled cars also receiving defective air bags.

At least 13 deaths worldwide have been linked to the defective air bags, whose inner workings are sensitive to moisture and can rupture, sending shrapnel flying toward the car’s passengers. The defect has also been linked to more than 100 injuries, many of them critical.

Fourteen automakers are recalling more than 60 million vehicles to fix the defect in the biggest and most complex recall in automotive history.

At the root of the problem is a compound called ammonium nitrate, which helps generate the gases that inflate the air bag. Ammonium nitrate breaks down over time when it is exposed to moisture or temperature swings and, when activated, can cause its metal casing to disintegrate.

Takata is the only major air bag maker that uses the compound in its driver- and passenger-side air bags.

Takata have been barred by auto safety regulators from entering into any new contracts for air bags that use ammonium nitrate and must phase out existing contracts.

Still, they remain free to equip model years already in production with the defective Takata air bags, including an older version of the air bag that does not contain a drying agent that helps protect their interior from damaging moisture.