Kg CO2 per litre

If you burn a litre of diesel this will produce around 2.62 kgs of carbon dioxide. Petrol has a lower carbon content and so produces around 2.39 kgs of CO2. The precise figures depend on the quality of the fuel. Since fuel weighs less than a kilogram per litre, it is interesting to see how the weight of emissions is multiplied by the addition of oxygen. The tables below show how the official test figures for CO2 emissions and combined MPG can be equated to see how individual vehicles perform in terms of CO2 per litre. Some cars appear to do better than the standard chemistry would suggest, whereas others do worse. So these figures show how inaccurate the testing mechanism can be, and how different engines skew the results. The official tests measure exhaust gases only and then calculate the fuel consumption.
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Top 10 CO2/litre petrol cars
Make	Model	Derivative	CO2 (kg)/litre	CO2 (gpkm)	Litre per 100km	MPG (combined)	List price
Audi	TT Roadster	1.8 TFSI 160PS	1.91	159	8.31	34	£23,915
Volkswagen	Passat Estate	1.8 TSI Highline 160PS Auto	2.12	178	8.41	34	£21,925
Volkswagen	Passat CC	3.6 V6 GT 300PS	2.17	219	10.09	28	£30,865
Mitsubishi	i	0.7 MIVEC Turbo Auto	2.20	114	5.17	55	£9,149
SEAT	Ibiza New	1.6 16V SE 105PS DSG	2.21	148	6.69	42	£12,460
SEAT	Ibiza SC New	1.6 16V Sport 105PS DSG	2.21	148	6.69	42	£12,350
SEAT	Leon	1.6 16V S	2.23	169	7.59	37	£13,490
Volkswagen	Scirocco	1.4 TSI 160PS DSG	2.23	147	6.60	43	£20,410
SEAT	Altea	1.6 Emocion S	2.25	173	7.70	37	£14,240
Nissan	Note	1.6 Acenta	2.26	149	6.60	43	£12,440
Bottom 10 CO2/litre petrol cars
Make	Model	Derivative	CO2 (kg)/litre	CO2 (gpkm)	Litre per 100km	MPG (combined)	List price
Toyota	Avensis Tourer New	1.8 V-matic T2	2.82	155	5.50	51	£17,585
Volvo	V70	2.5T (231PS) R-Design SE	2.77	244	8.80	32	£29,295
Mercedes-Benz	E-Class Estate	E 350 CGI Avantgarde G-Tronic	2.72	248	9.11	31	£39,719
Peugeot	308 5 Door	1.6 THP GT 136 FAP	2.65	146	5.51	51	£21,945
Peugeot	308 5 Door	1.6 THP Sport 175	2.64	180	6.81	42	£17,995
Mercedes-Benz	E-Class Estate	E 350 CGI Sport G-Tronic	2.64	248	9.38	30	£40,668
Mazda	Mazda RX-8	RX-8 R3	2.60	299	11.48	25	£24,478
Morgan	Roadster	3.0 V6 2-seater roadster	2.52	232	9.20	31	£36,641
Mercedes-Benz	A-Class Hatchback 5dr	A 180 Avantgarde SE Auto	2.52	166	6.60	43	£19,270
Audi	Q7	3.6 FSI quattro S Line	2.51	304	12.12	23	£43,135