SAN ANTONIO -- The noise of chatting parishioners saturates the foyer after the five weekend Masses at St. Mark the Evangelist Catholic Church.
Busy parents empathize with one another. Children find new playmates. Singles meet other singles.
The tangle of conversations helps the church's 5,000 worshipers to build a sense of community in a fast-growing congregation that decided five years ago to expand into a 1,500-seat sanctuary, rather than split into two separate congregations.
The move was an example of how Roman Catholic parishes are joining Protestant congregations across the country in creating megachurches, where thousands, sometimes tens of thousands, of congregants worship together.
But unlike the Protestant churches, which use evangelistic campaigns to grow, dioceses say that too few priests and too many worshipers drive their expansion.
While the number of worshipers per parish has grown by almost 35 percent in almost three decades, the number of priests dropped 26 percent, said Mary Gautier with the Center for Applied Research in the Apostolate at Georgetown University, which tracks trends in the Catholic Church within the United States.
''That's the reality in the Catholic Church today: You don't want to build something that will be OK for now, when you know this large population is going to get bigger," Gautier said.
Dioceses in the South and West, hot spots for new jobs and suburban sprawl, are primarily the ones building larger parishes; they're increasingly filled with Hispanic Catholics, many of them immigrants, Gautier said.
The Midwest and Northeast are generally consolidating, Gautier said, due largely to population shifts.
Gautier said several dioceses, including the Archdiocese of San Antonio, seek at least 1,000 seats in design plans for new or expanded sanctuaries. Most sanctuaries used to be built with about 500 seats, she said.
In San Antonio, at least 15 sanctuaries have doubled or tripled to at least 1,000 seats in the past eight years.
''We didn't want to put two parishes in the same town because we just didn't have the priests to do it," said the Rev. Monsignor Larry Stuebben, vicar general of the archdiocese.
Increasing the number of parishioners adds to a need for financial commitments but it also drives down the average cost per church member, according to the Georgetown research group.
The group estimates that it costs $444 per household nationwide for membership in churches with fewer than 800 parishioners, compared with $337 for those with more than 1,000.
The extra congregants help to cover the cost for larger paid lay staffs -- who are increasingly picking up administrative duties to free priests for pastoral and sacramental duties, said the Rev. Larry Christian, who is the rector of Assumption Seminary in San Antonio.
''You have to have a large enough economic base to make that happen," he said.
The Roman Catholic Church in the United States, which has 65 million members, has generally tried to avoid the ''megachurch" model, like Joel Osteen's Lakewood Church in Houston, which took over the former arena for the Houston Rockets NBA team and fills it each week with more than 30,000 congregants.
The US Conference of Catholic Bishops advises parishes to avoid ''any semblance of a theater or an arena" in worship settings.
While new Catholic churches have been designed with a larger seating capacity, the pews are curved around the altar so people don't lose a sense of intimacy during worship, said Jim Moroney, head of liturgy for the Catholic bishops conference.
''The challenges are indeed significant," Moroney said. ''But we want to create sight lines to see the whites in someone's eyes when we're preaching to them."
And large parishes are offering more programming, especially Bible study and social action groups, so members meet one another and create a community within a community, Moroney said.
That programming makes them more like Protestant megachurches, said Scott Thumma, who specializes in megachurch research at Connecticut's Hartford Seminary.
The 1,200 Protestant megachurches in the United States, megachurches being defined as having at least 2,000 weekly attendees, make small-group participation a crux of their organizational structure, he said.
''Anything that goes beyond just a large gathering -- such as using small groups to create a congregational life with their members, that's a significant shift in the organization of a Catholic congregation," Thumma said.
St. Mark advertises more than 40 ministries and small groups on a large sign over the main entrance to the sanctuary, including a Bible study that breaks members into groups of eight to 10.
''Once a person makes a connection by putting their name on a list or talking with a leader, then I feel its our responsibility to pick up on that," said the Rev. Kevin Ryan, the St. Mark pastor.
The church considered splitting into two congregations in the early 1990s because regularly 200 people would have to stand in aisles in its 750-seat sanctuary for weekend Masses, said a longtime member, Marybeth Green.