# The three-tier sampling procedure

> Explains the MDG 2024 three-tier sampling procedure for MS and HSD: daily samples at supply locations, tank lorry retention samples drawn by the dealer, the transporter's set, and random sampling by oil company officials.

Canonical: https://dipdensity.watsinfo.com/guides/three-tier-sampling-procedure/
Last updated: 2026-11-02

**Short answer:** Samples are kept at three points so any fuel can be traced to its source: the depot keeps daily samples, the dealer keeps a sealed sample from every tanker, and oil company officials draw samples from the pump nozzles. The dealer keeps the tank lorry samples of the last two loads for each tank.

## Why three tiers

MDG 2024 chapter 2 states the aim: to ensure that the petrol and diesel sold at an outlet is the same product its oil company supplied. Samples kept at each step let a dispute be settled by testing what was really loaded and delivered.

## Tier 1: at the supply location

Every day the depot keeps at least **4 × 1 litre of petrol and 2 × 1 litre of diesel** from the loading point, and again after switching storage tanks. Samples are labelled and kept for at least **30 days**. The invoice states the density at 15 °C, the loading point, the storage tank and the time the lorry left.

## Tier 2: the dealer's tank lorry sample

After the [density check](https://dipdensity.watsinfo.com/guides/density-variation-limit/) passes, and after draining at least 20 litres from each compartment:

- Draw **2 × 1 litre of petrol** and/or **1 × 1 litre of diesel** as bottom samples, in proportion to each compartment's quantity.
- Rinse the empty aluminium containers with the same product first.
- Seal and label them before unloading. **The dealer and the driver both sign** the label.
- Mark the storage tank the product went into, if there is more than one.
- Keep the samples of the **last two loads for each tank**.

The transporter may take a second set, paying for it and a deposit of **₹300 per container**.

## Tier 3: the oil company's samples

Officials, mobile labs and authorised agencies draw samples from the nozzles of every tank. Random sampling covers at least **2% of the network every month**, and samples are also drawn after a density failure, a filter paper failure, a stock variation beyond the limit, or a complaint. For petrol, **six 1 litre samples** come from each tank: two for the dealer, two for the office and two for the laboratory. Officials bring their own containers and pay for the fuel with a cash memo.

## Questions

### What if the tank lorry driver refuses to sign the sample label?

Do not decant. MDG 2024 says to contact the supply location or the sales officer.

### How many samples does an inspector take?

For petrol, six 1 litre samples from each tank: two stay with the dealer, two at the oil company's office, and two go to the laboratory.

## Sources

- [BPCL, Marketing Discipline Guidelines 2024](https://www.bharatpetroleum.in/images/files/MDG-2024-Effective-24-10-2024.pdf)