For the leading foursome on HBO’s “Entourage,” style so far has meant two things: jeans and T-shirts. Yet as the show concludes its third season, things are changing in the wardrobe department. As in real life, success leads to better clothes.

The plot of “Entourage” revolves around the movie star Vincent Chase (Adrian Grenier), who landed in L.A. with his best-buddyturned-manager Eric (Kevin Connolly), his narcissistic older brother Johnny “Drama” (Kevin Dillon), and his hip-hop trash-talking friend Turtle (Jerry Ferrara). In the 2007 episodes, Vince’s star is rising, which means there’s more on the line for Eric, as well. Drama — a has-been actor constantly looking for work — has re-entered the industry. Even Turtle is enjoying a slice of success as the manager of a young rap star. And so, the boys are dressing — if not growing — up. At least a little.

As the sleepy-eyed heartthrob, Vince has a free pass to dress as sloppily as he likes. Jeans hang loose on his slim frame. His Tshirts are sloppy, usually dark, and somehow dirtier than anyone else’s. “Vince has to really look like he doesn’t put a lot of thought into it. He’ll wear Gucci pants with an old beat-up T-shirt,” the show’s costume designer, Amy Westcott, said. “He’ll wear that just to hang out, especially if they have to go to an office. That’s his way of dressing up.”

Although jackets by Nicole Farhi and Band of Brothers are highend, Vince’s laid-back air takes the emphasis away from the expense. “It’s more important about the way it’s worn,” Ms. Westcott said.

This season will see Eric in fewer T-shirts and unconstructed blazers. As Vince’s best friend and manager, he’s stepping up to the plate — but not quite into suits. “He’s going to be more dressed up. He has to be taken more seriously and not blend in with the guys as much,” Ms. Westcott said. “We’re doing a lot more dress shirts, nice pants, dress shoes.”

Drama, too, wants to stand out from the bunch, but he does so with T-shirts and tank tops that show off his sculpted body. As the older, yet less successful, brother, he spends more time creating a look. “Drama is the most thoughtout of all four. He’s worried about how he is portrayed to the world,” Ms. Westcott said. “Now that that he’s employed, we’re putting some nicer things on him. He is a little trendier, and he can go out on a limb.”

As for Turtle, the look retains an East Coast urban flair, but a little more expensively so. “He’s holding on to his roots. He’s got the Queens thing going on,” Ms. Westcott said, adding that she works with Kangol and New Era to create hats that match his sweat suits. She also picks out the custom colors for his Air Force One sneakers.

Typically, the male actors select from pieces that Ms. Westcott has gathered together for them. But for the women on the show, the approach is more varied. Actress Debi Mazar, who plays Shauna, Vince’s public relations manager, is much more directly involved. Ms. Westcott and Ms. Mazar go on shopping trips together to Rodeo Drive. The results are suits by Gucci, Isabel Toledo, and Dolce & Gabbana, many of which emphasize a nipped waist and open neck.

Eric’s girlfriend, Sloan (Emmanuelle Chriqui), who is also the daughter of a mega-agent, is typically dressed as the ultimate L.A. hostess. “We try to give her individual taste, but also keeping her really upscale,” Ms. Westcott said.

The process of dressing Ms. Chriqui became a creative one for Ms. Westcott. “We were trying things, trying things, and everything was just okay. Then there was this great Michael Kors skirt, and we ended up using it as a dress,” Ms. Westcott said. “She’s game. She’ll try anything.”

The Kors dress is red and white and will be shown in the first episode, airing April 8. The new addition to the cast, Carla Gugino, who plays Vince’s new agent, will be wearing sexy power suits with camisoles to maintain a level of femininity. “She’s got a terrific body. Dolce & Gabbana fits her like a glove.”

As for Vince’s former agent, Ari Gold, the suits are classic and upscale: Cannali, Gucci, Domenico Vacca, Zegna, and Ted Baker. But for his assistant, Lloyd (Rex Lee), the go-to brands for suits are Brooks Brothers and Hugo Boss — worn with colorful shirt-and-tie combinations.

Ms. Westcott, who lives in New York and works on independent films here, says she has a “New York aesthetic” that helped her get the “Entourage” job. When she’s in New York, she finds herself shopping at Century 21, Bloomingdale’s, and boutiques all around town, especially Bleecker Street and NoLIta. But some work creeps in, too. “I use so much Theory on Eric, and they don’t have a store [in L.A.]”

Across the board, the costumes will draw more distinctions between the characters than ever, Ms. Westcott said: “I’m trying to keep things very defined this year.”