When California, New York, Texas and other states began deregulating their electricity markets in the 1990s, officials promised that those changes would foster competition and make energy more affordable.

But it hasn’t worked out that way.

Average retail electricity costs in the 35 states that have partly or entirely broken apart the generation, transmission and retail distribution of energy into separate businesses have risen faster than rates in the 15 states that have not deregulated, including Florida and Oregon. That difference has persisted for much of the last two decades or so, including in the last year, when energy prices increased worldwide after Russia invaded Ukraine.

On average, residents living in a deregulated market pay $40 more per month for electricity than those in the states that let individual utilities control most or all parts of the grid. Deregulated areas have had higher prices as far back as 1998.