The Nuka-Cola Challenge

 is a Fallout 3 side quest connected with the Nuka-Cola soft drink. It is also an Xbox 360 and PC achievement and a PlayStation 3 Trophy.

Warning: If this quest is completed before the unmarked quest Just for the Taste of It, Goalie Ledoux will not appear, making it impossible to complete.

Take Sierra's Nuka-Cola tour
To start this quest, find Sierra Petrovita at Girdershade, which is located west of Jocko's Pop & Gas Stop and SW of Smith Casey's Garage.

Upon finding Sierra Petrovita, she offers you to take the "Nuka-Cola tour," which consists of viewing the large number of Nuka-Cola collectibles she owns. If you agree to take the tour, she will show the player around her home, discuss various Nuka-Cola facts and talk about some of the items in the room. After the tour, she gives the player an Ice Cold Nuka-Cola.

Talk to Sierra
She then asks the player to collect Nuka-Cola Quantums and says she will pay 40 caps for each bottle.

After exiting her house, Ronald Laren will ask the player to instead give him the Nuka-Cola Quantums, as he hopes that giving them to Sierra will improve his chances of "plowing her bean field". He offers to pay the same price for the Quantums, though a successful Speech check will cause him to double the payment. If you have the Black Widow perk, you also have the option to offer a threesome in exchange for him finding the bottles, causing him to eagerly run off to his death. His body can then be found inside the main entrance of the Nuka-Cola Plant.

Recover 30 bottles of Nuka-Cola Quantum
Nuka-Cola Quantums are rare items. The best way to obtain them is to explore every room you go in. They are easy to see because they glow (only if HDR is enabled on the PC version). There is also a ten percent chance of finding one in a Nuka-Cola Vending Machine. For a list of bottle locations, please see Nuka-Cola Quantum.

Recover the shipping manifest (optional)
A good place to start looking is the Nuka-Cola Plant. Aside from a few Quantums, you can find a terminal entry with shipping details for Quantum. You can get the code for this terminal from Milo, Shipping Foreman by either passing a Speech check, killing it, obtaining an employee badge by finding the note Welcome to the Nuka-Cola Family! or by using a dialogue choice obtained through the Robotics Expert perk. The code is used in the computer terminal in the room where Milo is found. After using the code, select the option to retrieve the shipping manifest.

The manifest tells the player of three locations where shipments of the Nuka Cola Quantum were in the process of delivery; these being the shopping center at Paradise Falls, Super Duper Mart, and Old Olney grocery.

At the Super Duper Mart, the shipment of Nuka-Cola Quantum can be found in the back storeroom near the fallen shelves next to the Protectron. There are three of them. It is in the same room as the Emergency Supplies.

In Paradise Falls, the Quantum can be found in Eulogy's Pad underneath the stairs next to a bed. There are five of them. You should also be careful when stealing these Quantums, becuase if anyone sees you, the whole town will turn hostile towards you. It should also be noted that you will not lose Karma for stealing these as they are the property of Eulogy Jones, since he is a slaver and slavers are evil, you won't lose Karma for stealing it from him.

When investigating Old Olney, you will discover that the shipment of Quantum never made it there. The skeletal remains of the driver can be found on the steps outside a building in Old Olney along with the Nuka-Cola Accident Report. The note reveals that there was an accident and the driver abandoned the truck to look for help (which never came because the bombs fell). The truck with its Nuka-Cola Quantum can be found by exploring the highways surrounding the town. It is underneath a highway about halfway between Old Olney and Chaste Acres Dairy Farm. There are six to eight of them. Beware of this truck though. There have been reports of Raiders, Giant Ants, and Deathclaws near the truck.

Reward
Sierra pays you for the Nuka-Cola Quantums (40 caps each). Once you give her enough to fill her Nuka-Cola Vending Machine, she gives you the Schematics - Nuka Grenade, and you get +300 XP. In the future, she will also make you a Mississippi Quantum Pie if you bring her the ingredients.

Giving the bottles to Ronald Laren results in a loss of karma and double the caps (80 caps each) if you succeed in the Speech check, otherwise you get 40. Once the quest is complete (if you gave him 30), he goes to Sierra's house straight away and starts making moves — only to have Sierra completely misunderstand his advances.

For maximum money and good karma, it is possible to give 29 bottles to Ronald, and 30 to Sierra, or vise versa for bad karma. However, a total of 59 bottles is a difficult achievement and will make it very hard to make any Nuka Grenades or Mississippi Quantum Pies, as Nuka-Cola Quantums are semi-rare. (Although if you have the Broken Steel add-on and have the Quantum Chemist perk and possess many Nuka-Colas, it is possible that you can make many Nuka Grenades-especially since Nuka-Cola is restocked in traders inventories every so often)

Behind the scenes

 * The name of this quest is a reference to "The Pepsi Challenge," a taste-test marketing promotion run by PepsiCo since 1975.
 * If Sierra is killed, and Ronald is spoken to, a Speech check can be passed in which the player blames the Nuka-Cola Corporation for her death. Ronald will assume it's because the Nuka-Cola machine he got for her had a label saying; "Warning if you tamper with this unit you'll have to answer to the Nuka-Cola Corporation". This dialogue is likely a reference to a scene from the film Dr. Strangelove involving tampering with a Coca-Cola machine.

Bugs

 * If the player starts the quest and immediately gives Sierra all 30 bottles, she may only give the player 40 caps in total, rather than 1200 caps as she should. The Nuka-Grenade Schematics may also not be given. Despite this, it will still count as completion of the quest. Leaving dialogue and talking to her again remedies this quirk.
 * Similarily, Ronald may not pay for the Quantums if they are given to him.
 * If this quest is completed before the unmarked quest Just for the Taste of It, Goalie Ledoux will not appear, making it impossible to complete.
 * Random enemies may spawn in Sierra's house. Among the guests include Sentry Bots, Deathclaws, Giant Radscorpions, and even Enclave troops. If this happens, if they are not killed quickly, Sierra will be killed, failing the quest.(PC)
 * The quest never updates after you get the manifest from the Nuka-Cola Plant Factory Floor.
 * If Ronald is sent to the Nuka-Cola Plant with the 'Black Widow perk', and the player immediately fast-travels there and kills all the security Protectrons on the first floor, he won't die. He'll appear inside the plant later, alive and well, standing near the front door.
 * If you leave Sierra's House, a live Brahmin at the outside will appear dead with no apparent reasons, even though you just enter the house for a few seconds and go out after that. It could probably be killed by the other animals, such as Mole Rat or Radscorpion, but there are no other animals at the moment you enter the house.