You are correct; it's rió.

There is a verb conjugator on this site, see below. You put in the verb you want conjugating.

[url=http://my.spanishdict.com/lessons/page/show'id=1710195%3APage%3A3370]http://my.spanishdict.com/lessons/page/show'id=1710195%3APage%3A3370[/url]

I have just entered the verb and the third person preterite is reyó. Are there two variations.

I have just checked Linguaphone and they say it is rió. Looks like our verb conjugator may be wrong.

Hola Eddy,
Sorry but I did enter the verb "reir" at the conjugator as you recomended, and i have discovered many other wrong for this verb, such as subjunctive imperfect and indicative, future, imperative and gerunde.
I would like to recomend La Real Academia Española conjugator (http://www.rae.es/rae.html), when you enter any verb, you will get, in addition to the definition, the word "conjugar" at the left side, it's very complete and accurate.

Thanks in advance, if you have any correction for me.

Quite true, the verb is completely wrong, all over mind you.

Hi Vernic
I have tried this link and whilst it goes to the rae web site, I can see no verb conjugator after searching for a verb.

Conjugar is to the left of the verb after you search it.
On La Real Academia Española conjugator it has rio

Is this a mistake or is there no accent'

This is becoming interesting!

There seems to be some confusion among native speakers, and even among reference works. However, the RAE, unsurprisingly, seems to be correct that there is no accent. And here's why.

When there is one strong vowel (a, e, o) and one weak vowel (i, u) together they make a diphthong (one syllable), and the syllable stress goes on the strong vowel. In this case, the O is strong and the I is weak, so rio already takes stress on the O by default.

The reason for the confusion may be that the word río (river) is an exception, and therefore requires an accent. Furthermore, the same problem seems to exist for similar verb conjugations, such as dio (perterit of dar).

I therefore retract my initial post, and change my stance to agree with the RAE that rio is correct.

I'm glad this question was asked!

eddy, You have to search for the verb, and at the result tab, to the left of the verb is "conjugar".
Hola Jich, I didn't notice before, but all right, (indicative preterite shows rio instead rió).

Oh, oh, oh, James, mi más sincero reconocimiento, como hispanoparlantes, no ignoramos, pero generalmente olvidamos estas reglas gramaticales, lo cual no me enorgullece, pero gracias por llegar al rescate.

For what it's worth, my Oxford Spanish dictionary, 94 edition, (which has been quite reliable over the years) lists the conjugation explicitly as rió.