The Repsol board has been "very divided," and Pemex's departure "could be positive in the medium term," he added.
Shares in Repsol, which were suspended from trading ahead of the announcement of the stake sale, closed down 3.6% at 20.11 euros, just above the price of the placement of 20.10 euros per share.
The stock was the biggest loser in the Ibex-35 index of most traded shares, which closed down 0.2% overall.
"In the medium term we feel that Pemex's exit is favorable since it was a source of instability in Repsol's ownership [that] has been eliminated," equity analyst Sonia Ruiz de Garibay of Beka Finance wrote in a research note.
Copyright Agence France-Presse, 2014