The following was spoken by Suta Goswami and taken from the Book Ekadasi compiled by Krsna Balaram Swami. (please forgive any typos)
Benefits of observing Ekadasi:
Arjuna the son of Prtha asked the Lord O Janardana what are the pious benefits of complete fasting, eating only supper, or eating but once at midday on Ekadasi, and what are the regulations for observing the various Ekasasi days, Kindly narrate all this to me.
Please listen as I now describe the results obtained by one who observes Ekadasi in this way. Neither the merit one receives by taking a bath in the sacred place of pilgrimage known as Sankhodara, where the Lord killed the Sankhasura demon, nor the merit one receives upon seeing Lord Gadadhara directly is equal to one sixteenth of the merit one obtains by fasting on Ekadasi. It is said that by giving charity on monday when the moon is full, one obtains a hundred thousand times the results of ordinary charity. O winner of wealth, one who gives charity on the day of the sankranti (equinox), attains four hundred thousand times the ordinary result. Yet simply by fasting on Ekadasi one obtains all these pious results as well as whatever pious results one gets at Kuruksetra during an eclipse of the sun or moon. furthermore, the faithful who observes complete fasting on Ekadasi achieves a hundred times more merit than one who perfoms an Asvamedha yajna (horse sacrifice). One who observes just a single Ekadasi perfectly earns the same merit as one who feeds a hundred thousand mendicants each day for 60 thousand years. And a person who properly observes Ekadasi just once earns ten times more merit than a person who gives a thousand cows in charity to a brahmana learned in the Vedas.