The petition was also sent on Sunday to 15 leading members of the Al-Saud ruling family, including Crown Prince Sultan bin Abdul Aziz and Interior Minister Prince Nayef, writer Mohammed bin Hudeijan al-Harbi told AFP.
The signatories, who call themselves "advocates of a civil society" and include five women, demanded the introduction of a parliament "elected by all adults, men and women" in ultra-conservative Saudi Arabia.
As a first step, they proposed electing half the members of the Shura Council, an all-male advisory body whose 150 members are named by the king.
They demanded the promulgation of laws to "combat poverty" and institute a fair distribution of resources, complaining of a "huge disparity" in apportioning the kingdom’s vast wealth.
The reformists called for "issuing a code recognizing the rights granted by sharia (Islamic law), which guarantees freedom of opinion, expression and assembly."
Other demands included the promulgation of an "effective law" regulating the creation of independent civil associations.
They also called for moves to enhance the independence of the judiciary such as open trials, and the separation of the powerful interior ministry into two ministries — one in charge of local government and the other of security.
The signatories, from different walks of life, included some of the dozen activists who were arrested in March 2004 after putting their names to a petition also demanding a constitutional monarchy.
Three of those were put on trial and spent 17 months in jail before being pardoned by Abdullah when he rose to the throne in August 2005 after the death of King Fahd.
"We believe that King Abdullah is the most prominent advocate of reform in Saudi Arabia," Harbi said, explaining why the signatories thought they stood a better chance than before of eliciting a sympathetic response.
"Our demands confirm the legitimacy of the honorable ruling family and propose public and peaceful action to … build a modern state based on an Islamic constitution," Harbi said.
However, he said, the signatories decided to send the petition by mail rather than request an audience with the king because past experience suggested they stood little chance of being granted a meeting.
It was not immediately clear if the message had already reached the king.
Harbi said four of the signatories were in detention and he believed they had been arrested as "a preemptive strike against the statement."
Three of those detained were among 10 people arrested in early February whom the interior ministry said at the time were held on suspicion of collecting money to fund terror-related activities.
"Everything is possible," Harbi said when asked if he did not fear further arrests.
Saudi Arabia has a basic statute of government based on sharia, which serves as a constitution.
The oil powerhouse has under Abdullah, who was de facto ruler for 10 years before becoming king, taken small steps toward reform, including male-only elections to pick half the members of municipal councils in 2005.
