Web addresses ending in .xxx have gone on general sale, as legal efforts continue to scupper the domain name.
Some 100,000 addresses have already been purchased in a restricted sale. The first pages went live in September.
Two of the net's biggest pornography firms have accused ICM Registry - which oversees the addresses - of being "anti-competitive" and a "monopoly".
ICM Registry said that lawsuits are "without merit" adding that it plans to defend itself.
Manwin Licensing and Digital Playground claim that the decision to create .xxx is flawed and that ICM Registry had abused its position. They are suing the Internet Corporation for Assigned Names and Numbers (Icann), which oversees web addresses, and have also filed a lawsuit against ICM Registry.
The public sale of the domain follows years of wrangling over whether a specific adult content address was needed. The move was finally approved in March by Icann.
The decision ended a decade-long battle for the move by ICM Registry which was awarded the right to administrate the new domain. It put .xxx on a par with more conventional web addresses such as .com and .org.
"It has been 10 years in the coming and today the floodgates are open," said ICM Registry chief executive Stuart Lawley.
"We would hope that the number of domains sold will more than double very quickly," he added.
Manwin - which runs the Playboy websites - claims that ICM Registry was charging annual fees of about $60 (£38) per address, which it said was 10 times the fee charged for other comparable top-level domain names.
But Mr Lawley said that its pricing "was comparable with other niche providers".
"There are economies of scale here, bear in mind that .com sells 100 million names a year," he told the BBC.
He added that the current lawsuits were "without merit".
"We will contest them vigorously. There are some incumbents who would like to keep the status quo but how can a top-level domain name be anti-competitive?" he said.
ICM Registry is confident that the new address will "act as a responsible alternative for adult content sites".
It claims that .xxx sites will be safer than traditional pornography sites, partly because they will benefit from daily malware scanning from security firm Macafee.
It also contracted software developer Metacert to develop safety labels which it said would make it easier for users, especially parents, to adjust their browser settings to restrict access to such sites.
Some 250 million pages of adult content across all domain names had already been labelled using the system, it said.
Its .xxx website, which details how interested parties can register their domain, has received nearly one million visitors. The website lists all the registrars. Prices will be set by the individual registrars.
Companies and individuals that do not want their name associated with pornography will be able to pay a one-off fee of between $150 and $300 (£100 to £200), depending on which company they register their domain with.
For example, UK adult star Teresa May might wish to bid for a .xxx domain, whereas UK home secretary Theresa May might consider protecting her name.