* To register with U.S regulator to sell block of shares
* Stake would be sold on markets
* Aims to speed up Argentine disinvestment
* Wants to invest elsewhere (Adds background)
MADRID, Nov 25 (Reuters) - Spanish oil major Repsol YPF said it is preparing to sell up to 15 percent of its Argentine unit YPF in the markets, speeding up its partial exit so it can redirect money to less mature markets.
Repsol said on Thursday it will register with the United States securities regulator to sell the YPF shares.
Repsol has only had the option until now to sell small packets of shares, but the registration will allow it to accelerate the process by selling off larger pieces.
YPF is profitable but Repsol would like to reduce its large stake -- 84 percent -- and use proceeds to invest in other markets with less mature fields, such as Brazil.
"The aim is to be more agile....to be able to sell YPF shares according to demand," a Repsol spokesman said.
Repsol has reiterated on several occasions that it plans to cut its stake in YPF, partly through a stock market listing, while always retaining at least 50 percent.
YPF controls more than half of Argentina's refining capacity and nearly 40 percent of its oil output.
About 15 percent of YPF is in the hands of Argentine businessman Enrique Eskenazi who has an option which expires in 2012 to buy a further 10 percent.
Although Repsol has good relations with the Argentine government, the energy sector in general has chafed at price controls and state intervention in the South American country.
The sale would be for a maximum of 58,996,919 shares or the equivalent in American Depositary Shares, and the exact number, timing or mechanism will be determined later, Repsol said in a statement through the Spanish and Argentine securities regulators.
(Reporting by Andres Gonzalez; Writing by Fiona Ortiz; Editing by Erica Billingham)